TL;DR:

In general, the perspective of the Imperial leadership can be broken down into a few broad categories. In order of how common each of these attitudes were, from most common to least, the categories are:

• "We're not evil. We're committed to establishing law and order, and a more equitable social structure than the Republic ever managed to create. Even if we are forced to maintain control by using force and instilling fear, the ends justify the means."

  • The default position of almost all the highest ranking Imperials, echoed by many of their underlings.

• "We're the good guys, even though we sometimes do bad things. We only do bad things when the bad guys (i.e., everyone who opposes us) force us to. And however bad the things we do might be, we're still better than the bad guys. And of course, if the bad guys didn't keep causing trouble, we'd never do anything remotely unpleasant."

  • Probably most common among mid-tier and rank-and-file Imperials who had been indoctrinated into the Imperial mindset and didn't question it.

• "We're the goo... Wait, we just did WHAT? Okay, that's clearly evil, and we're obviously the bad guys, so I quit."

  • Less common than the previous categories, but more common than you'd think. This was the path adopted by former Republic loyalists who tried to maintain their allegiance after the creation of the Empire, but were intellectually honest enough to accept the growing evidence that the Empire was inherently evil.

• "We're totally the good guys. Wait, we just lost the war? Those rebel scum. Wait, we did WHAT during the war? And the Emperor was actually a WHAT? Oh... I guess we really were the bad guys. Crap. I didn't know, I swear!"

  • For many in the Imperial rank-and-file, the conviction that the Empire was good remained intact until after the war ended and the Empire's atrocities could finally be brought to light. Many people who had formerly fit in one of the previous categories now found themselves in this one.

• "We're evil, and that's awesome, but our ultimate goals include elements that will benefit the masses, like law and order... Still, we're also in this for ourselves."

  • Very rare indeed - I've only found one or two people who clearly belong in this bizarre category: Yupe Tashu (see below) and Darth Vader. And the former was largely a fraud, trying to be something he really wasn't. As such, it is possible that Vader alone fits this category.

• "We're evil, and that's awesome - no qualification, no higher purpose, just evil. Screw law and order - that's just a cover story. Really, this is all about power and bending an entire galaxy to the will of one man. Nothing else matters."

  • This was the most honest appraisal of the Empire, and only one person subscribed to it: Palpatine himself. Everyone else was doing his bidding, and although no one realized it, everything they did was designed to cement his position and enable him to obtain his real goal: to become a god and enslave the galaxy.

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Most Imperials didn't consider themselves to be evil:

Here's how Moff Tarkin described Imperial history in his memoir:

The factor that contributed most to the demise of the Republic was not, in fact, the war, but rampant self-interest. Endemic to the political process our ancestors engineered, the insidious pursuit of self-enrichment grew only more pervasive through the long centuries, and in the end left the body politic feckless and corrupt. Consider the self-interest of the Core Worlds, unwavering in their exploitation of the Outer Systems for resources; the Outer Systems themselves, undermined by their permissive disregard of smuggling and slavery; those ambitious members of the Senate who sought only status and opportunity.

The reason our Emperor was able to negotiate the dark waters that characterized the terminal years of the Republic and remain at the helm through a catastrophic war that spanned the galaxy is that he has never been interested in status or self-glorification. On the contrary, he has been tireless in his devotion to unify the galaxy and assure the well-being of its myriad populations. Now, with the institution of sector and oversector governance, we are in the unique position to repay our debt to the Emperor for his decades of selfless service, by lifting some of the burden of quotidian rulership from his shoulders.

By partitioning the galaxy into regions, we actually achieve a unity previously absent; where once our loyalties and allegiances were divided, they now serve one being, with one goal: a cohesive galaxy in which everyone prospers. For the first time in one thousand generations our sector governors will not be working solely to enrich Coruscant and the Core Worlds, but to advance the quality of life in the star systems that make up each sector — keeping the spaceways safe, maintaining open and accessible communications, assuring that tax revenues are properly levied and allocated to improving the infrastructure. The Senate will likewise be made up of beings devoted not to their own enrichment, but to the enrichment of the worlds they represent.

This bold vision of the future requires not only the service of those of immaculate reputation and consummate skill in the just exercise of power, but also the service of a vast military dedicated to upholding the laws necessary to ensure galactic harmony. It may appear to some that the enactment of universal laws and the widespread deployment of a heavily armed military are steps toward galactic domination, but these actions are taken merely to protect us from those who would invade, enslave, exploit, or foment political dissent, and to punish accordingly any who engage in such acts. Look on our new military not as trespassers or interlopers, but as gatekeepers, here to shore up the Emperor’s vision of a pacified and prosperous galaxy.
- Star Wars: Tarkin

Tarkin, like most Imperials, tended to overlook the excesses committed by the Empire, preferring to focus on the triumph of "law and order" over the indulgence and corruption of the Republic:

But perhaps it was enough to know that law and order had finally triumphed over corruption and indulgence, which had been the hallmarks of the Republic.
- Star Wars: Tarkin

Sometimes, they were forced to make their own excuses when confronted with Imperial brutality. In the Clone Wars, the Separatists had captured a moon called Antar IV. Republic spies were sent to the moon to foment dissent and resistance to the Separatists, and soon led thousands of pro-Republic guerrillas. When the Clone Wars ended with the defeat of the Separatists and the foundation of the Empire, Palpatine ordered the moon's inhabitants to be arrested and executed for treason. The Republic (now Imperial) spies on the moon asked for permission to extract their guerrillas, who - after all - had remained loyal, and fought the enemy at great risk to themselves, but the request was denied, and Imperial troops killed everyone on the moon, regardless of which side they had fought for. Tarkin supported and agreed with this move - which would later be known as the Antar Atrocity - but also understood, in an intellectual sense, why so many of the Imperial/Republic spies on the moon defected after the slaughter began:

The Imperial directive to make an example of the moon had made perfect sense to Tarkin at the time. He wasn’t a retributionist; it was simply that separating friend from foe would undoubtedly have allowed many Separatists to flee into hiding. Eliminating them en masse on Antar 4 was preferable to having to hunt them down later, in whatever remote regions they found shelter. His actions had conveyed a message to other former CIS worlds that defeat didn’t grant them absolution for their crimes, or assure them that the Empire was ready to welcome them back into the fold with open arms. The message had to be made clear to Raxus, Kooriva, Murkhana, and the rest: Surrender all former Separatists, or suffer the same fate as the population of the Gotal moon.

Still, Tarkin could see how a Republic officer like Teller might feel betrayed to the point where he would attempt to wage a campaign of revenge against all odds. The military was filled with those who refused to accept that collateral damage was acceptable when it served to further the Imperial cause. In the absence of order, there was only chaos. Did Teller expect an apology from the Emperor? Compensation for the families of those who had been unjustly executed? It was witless thinking. Multiply Teller by one billion or ten billion beings, however, and the Empire could face a serious problem...
- ibid

Although Tarkin once said that the Imperial approach was evil, albeit for rhetorical purposes:

"And this time you’re going to crush your opponents before they have a chance to organize.”

“That’s called pacification, Captain," said Tarkin.

"It’s rule by fear. You’re not just demanding submission, you’re generating evil.”

“Then evil will have to do.”

Teller stared up at him. “What transforms a man into a monster, Tarkin?”

“Monster? That’s a point of view, is it not? I will say this much, however: This place, this plateau is what made me.”
- ibid

Imperial leaders were comfortable with the idea of maintaining power by instilling terror in their subjects, because they believed it was all for the greater good:

Tarkin resumed his stance. This was how the Empire would conquer and rule, he thought: through might and fear... Tarkin was taking the massive ship right into the middle of it, placing not only himself but his own pilots and everyone else in peril.
- Star Wars: Tarkin

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Some Imperials thought they were the good guys, even though they sometimes did bad things:

The old Ahia-Ko people believed the water was so pure, it could take from you your sins and leave you a better person.

If only that were true.
- Imperial Admiral Rae Sloane's thoughts while showering, Aftermath

And:

“Why be a rebel? Why join?”

“To destroy the Empire.” She shakes her head.

“No. Too easy. That’s just the paint. Scratch off the color, there’s something personal underneath it.”

He again shows her his teeth—bared in a terrible smile. “Of course there is, Admiral. The Empire hurt people close to me. Family. Friends. A girl I loved, once. And I’m not alone. All of us in the New Republic, we all have stories like that.” He coughs. His eyes water. “We’re the harvest of all the horrible seeds you planted.”

“But we kept order in a lawless galaxy.”

“And you did it with a closed fist instead of an open hand.”

“You have a way with words for just a pilot.”...

The woman nods, and then turns and leaves without another word.
- Imperial Admiral Rae Sloane and her captive, Wedge Antilles, Aftermath

Note that Sloane doesn't disagree with Antilles' assessment vis á vis the Empire's closed fist.

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One Imperial appeared to embrace evil, but admitted that his support of Imperial brutality was partially motivated by the desire for "law and order":

Yupe Tashu, a non-Force-user, fancied himself a historian and occultist of the Sith, and served as an advisor to Palpatine. After the deaths of Vader and Palpatine, he continued to wax poetic about the virtues of the Sith, but he was essentially a fraud and a lackey.

It’s not just about law and order. It’s about total control. We will always come back for it. No matter how hard you work to beat us back, we are an infection inside the galaxy’s bones. And we will always surge forth when you least expect it.
- Yupe Tashu, advisor to Emperor Palpatine, Aftermath

He says this to Wedge Antilles, his captive; when Wedge responds by threatening to kick his teeth in, Tashu gleefully replies:

A vital spike of anger and hate. Born of the hopelessness I’ve planted in you. A terrible little seed. I can’t wait for it to grow its wretched tree and bear its ugly fruit.
- ibid

For all his efforts to convince others that he was essentially an acolyte of the Sith, he still comes across as a phony. Like almost all Imperials, he ultimately justified the Empire's brutality by appealing to the greater goal of law and order. Still, he - unlike the vast majority of his fellow Imperials - acknowledged that the Empire was also interested in power for its own sake.

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Some Imperials realized that they had been the bad guys after they were defeated at Endor:

“This isn’t some kind of inspirational story. Some scrappy, ragtag underdog tale, some pugilistic match where we’re the goodhearted gladiator who brings down the oppressive regime that put him in the arena. They [the Rebel Alliance/New Republic] get to have that narrative. We are the ones who enslaved whole worlds full of alien inhabitants. We are the ones who built something called a Death Star under the leadership of a decrepit old goblin who believed in the ‘dark side’ of some ancient, insane religion.”
- Imperial General Jylia Shale, Aftermath

And:

The Empire had little interest in learning the ways and tongues of other cultures. They didn’t even want their people to learn on their own time.

(Sinjir is reminded of the time he found the young officer studying Ithorese, of all things. That young, fresh-faced fellow, sitting cross-legged on his cot, a long index finger scanning lines of the alien script. Sinjir broke that finger for him. Said it was better than any administrative punishment—and faster, too.)

(Sinjir is also reminded: I am a terrible person. Guilt and shame duel in his gut like a pair of hissing Loth-cats.)
- Former Imperial Loyalty Officer Sinjir Rath Velus, ibid

But of course, others didn't, and accused their opponents of being the evil ones:

The rebels—because that’s what they are, rebels, criminals, deviants — did what they did with almost no war machine in place. Insurgents, all of them.
- Moff Pandion, ibid

And:

“Is this who we are now? Reduced to common hostage-takers? Perhaps the Galactic Empire truly is fading, like a star gone bright and then soon to dust. At least with the likes of you at the helm.”
- Moff Pandion, ibid

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Sometimes, a previously loyal Imperial learned of something so horrible and wicked that they could no longer deny the evidence that the Empire was evil.

In such situations, they would often defect - sometimes en masse. An enormous increase in defections from the Empire took place shortly after work began on the first Death Star, with countless scientists and technical personnel fleeing the base where the battle station was being built:

Motivated by grievances against the Empire, many had fled and become fugitives. The count was so high, in fact, that COMPNOR had compiled a most-wanted list of missing scientists and technicians who had held high-priority security clearances. The disappearances were often offered up as an explanation for harassment attacks against Imperial bases and installations.
- Star Wars: Tarkin

This passage, which comes just after the description of the Antar Atrocity, paints a compelling picture: Erstwhile Imperial loyalists had their confidence in the regime shaken by the mass murder of friend and foe alike on Antar, and were then deployed to begin work on an unprecedented weapon that would enable the Empire to commit genocide on an even larger scale. This created a nightmarish scenario in which a regime that was clearly willing to perpetrate unthinkable atrocities would have the means to do so on a mere whim. Such a prospect was too much for many Imperial personnel to ignore, and so they abandoned their previous allegiance to the Empire and either went into hiding or became active in the movements that would later coalesce into the Rebel Alliance.

This also happens in the new Disney Canon novel Lost Stars. A highly regarded Imperial officer named Thane Kyrell despises the Rebellion until he witnesses the destruction of Alderaan firsthand; his faith in the Empire is shaken. He is then deployed to a Spice mining world called Kerev Doi, where he discovers that the Empire has enslaved the entire Bodach'i species to punish them for resisting Imperial rule. He defects that night.

When the Imperial brass realize that Kyrell has gone AWOL, the Imperial Security Bureau interrogates his friends. The ISB agent says:

“He’s not the only one who lost people,” Ronnadam snapped, but then his expression grew more thoughtful. “And he’s not the only officer we’ve seen falter. The same offenses that would have gotten a man cashiered two years ago are now handled on a case-by-case basis... for now. There will of course be a penalty to be paid, but if Lieutenant Kyrell returns to duty in short order, he can continue his career without undue difficulty.”
- Star Wars: Lost Stars

Clearly, so many Imperial troops defected after the destruction of Alderaan that the Empire was forced to be lenient in its handling of defection, in the hopes of getting some of these valuable personnel back.

In short, it was possible for an Imperial to realize that the Empire was evil, but most people who had such an epiphany ceased to be Imperials shortly thereafter.

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Of course, there was one Imperial who knew that the Empire was evil to the core, and rejoiced in its depravity and cruelty, without any pretenses of serving a greater good:

Emperor Palpatine.

Eventually the dark side would grant him infallible foresight, but until such time future events would remain just out of clear sight, clouded by possibilities and the unremitting swirlings of the Force. He had made himself lord of all he surveyed, but he had much to learn. Actions meant to topple him from his lofty perch wouldn’t end with the successful containment of this most recent fiasco. But he would deal with any who chose to challenge him with the same precision he had applied to exterminating the Jedi. And he would not allow himself to be sidetracked from his goal of unlocking the secrets many of the Sith Masters before him had sought: the means to harness the powers of the dark side to reshape reality itself; in effect, to fashion a universe of his own creation. Not mere immortality of the sort Plagueis had lusted after, but influence of the ultimate sort.

As his Empire swelled, bringing more and more of the outer systems into its fold, so too would his power unfurl, until every being in the galaxy was held captive in his dark embrace.
- Star Wars: Tarkin

Even Vader seems to have had nobler purposes in mind at times - order, an end to conflict, and an aversion to destruction:

With our combined strength, we can end this destructive conflict, and bring order to the galaxy!
- Darth Vader to Luke, The Empire Strikes Back

But Palpatine, and only Palpatine, knew that the goal wasn't law and order, or an equitable social structure, or peace; the goal was simply to control the galaxy and make himself a god.

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Regarding the names used by the Empire for their military matériel:

The idea that the name "Destroyer" suggests willful evil just doesn't make sense. A Destroyer is a type of naval vessel in the real world, and "Star Destroyer" presumably means "Destroyer that does stuff in space instead of in the water".

In naval terminology, a destroyer is a fast maneuverable long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller powerful short-range attackers. They were originally developed in the late 19th century as a defence against torpedo boats, and by the time of the Russo-Japanese War in 1904, these "torpedo boat destroyers" (TBD) were "large, swift, and powerfully armed torpedo boats designed to destroy other torpedo boats." Although the term "destroyer" had been used interchangeably with "TBD" and "torpedo boat destroyer" by navies since 1892, the term "torpedo boat destroyer" had been generally shortened to simply "destroyer" by nearly all navies by the First World War.

Before World War II, destroyers were light vessels with little endurance for unattended ocean operations; typically a number of destroyers and a single destroyer tender operated together. After the war, the advent of the guided missile allowed destroyers to take on the surface combatant roles previously filled by battleships and cruisers. This resulted in larger and more powerful guided missile destroyers more capable of independent operation.
- Wikipedia

Naval vessels are intended for use in war, and war is about destruction. It would be ridiculous to call a combat vessel a "Hugs and Kisses Ship", because it is designed to destroy other ships, not cuddle with them.

Of course "Death Star" still strikes most people as a much more frightening, vicious, and unapologetically aggressive name, and - as explained above - many formerly loyal Imperials defected when they learned of the plans to build the first Death Star. But I suspect that the Emperor's stance was, at least in part, "Once I have a Death Star, I can afford to lay my cards on the table, because... wait for it... BECAUSE I WILL HAVE A DEATH STAR. By the time people hear about it and get upset, I'll be able to blow their planets up if they complain, so who cares what people think?".

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Update:

In the new canon novel Bloodline, Leia's thoughts about this subject are revealed:

“At the beginning of the war against the Empire, just as the Imperial Senate was dissolved—” She swallowed hard. “My ship was captured by the Devastator. That was Darth Vader’s flagship at the time. He personally brought me to the Death Star, where he— where he questioned me.”

Comprehension dawned in Casterfo’s eyes. “You mean…” Just say it. “I mean he tortured me, for hours. While a couple of his Imperial stormtroopers watched.” Sometimes that got to her when nothing else did. The troopers had been soldiers of the line. Some of them had honestly believed they were doing the right thing, or so she told herself.

But how could you believe that after you watched a nineteen-year-old girl writhing on the floor and screaming for mercy that never came? How could you stand there and watch that girl convulse in helpless agony without doing something, anything to help?

Apparently some people could.
- Star Wars: Bloodline, Claudia Gray

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