Is there a single word for an idea that receives acceptance not due to approval, but because opposing it is risky?

If you are choosing one option as the default out of not a choosing risky option, then you are minimizing risk by being circumspect.

[Merriam-Webster]
: careful to consider all circumstances and possible consequences : PRUDENT
// diplomacy required a circumspect response
// They are circumspect in all their business dealings.

In the context of the question, the following would be an appropriate sentences:

• New corporate politics required a circumspect policy.
• Employees, not wishing to appear unsympathetic to the new diversity program, made the circumspect decision to remain silent.

I suggest acquiescence.

Acquiescence (noun): The reluctant acceptance of something without protest.

Example: in silent acquiescence, she rose to her feet. [Lexico]

The verb for that would be acquiesce which means to accept something reluctantly but without protest.

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Or try preference falsification.

Preference falsification is the act of communicating a preference that differs from one's true preference. The public frequently convey, especially to researchers or pollsters, preferences that differ from what they truly want, often because they believe the conveyed preference is more acceptable socially. [Wikipedia]

(Groupthink, pluralistic ignorance, capitulate and the lesser of two evils could also work here.)

It doesn't really suit your specific example, but for instance when a company implements a crazy policy because all competitors are doing it as well, you could call it a fomo-policy (Fear Of Missing Out policy)

Expedient is the most appropriate word that comes to mind.

Merriam-Webster
characterized by concern with what is opportune
especially : governed by self-interest

Collins
If it is expedient to do something, it is useful or convenient to do it, even though it may not be morally right.

Or possibly qualified as politically expedient

Bowing down to a powerful group on grounds of expediency rather than because it's the right (or even most beneficial, in the long term, for the complying group/s and others) thing to do is called appeasement.

appeasement [noun; non-count] [formal; disapproval]

Appeasement means giving people what they want to prevent them from harming you or being angry with you.

He denied there is a policy of appeasement.

[Collins CoBuild; reformatted]

The claim that Churchill denounced appeasement when Nazi Germany was the threat with

An appeaser is one who feeds a crocodile — hoping it will eat him last.

is making liberal use of paraphrase (while being essentially accurate) (and very snappy). [Quote Investigator]

Politically correct, and politically incorrect

A company introduces a diversity program (something that may be considered as "politically correct") which will clearly disadvantage all of its current employees, but no one objects to it (because such opposition may be considered "politically incorrect") for fear of being called a racist.

OED

politically correct adj. (a) appropriate to the prevailing political or social circumstances (in early use not as a fixed collocation); (b) spec. (originally U.S., sometimes depreciative) conforming to a body of liberal or radical opinion, esp. on social matters, usually characterized by the advocacy of approved causes or views, and often by the rejection of language, behaviour, etc., considered discriminatory or offensive (cf. correct adj. Additions); abbreviated PC.

1798 A. J. Dallas Rep. Cases U.S. & Pennsylvania 2 462 Sentiments and expressions of this inaccurate kind prevail in our..language... ‘The United States’, instead of the ‘People of the United States’, is the toast given. This is not politically correct.

1970 T. Cade Black Woman 73 A man cannot be politically correct and a chauvinist too.

2001 Guardian 25 Aug. i. 13/1 Teenage boys are at the least politically correct stage of their lives.

politically incorrect adj. not politically correct; flouting liberal convention; discriminatory.

1876 J. Routledge Chapters Hist. Pop. Progress ii. 28 Politically incorrect, the clergy were socially in accord with the amenities of English life.

1939 New Republic 9 Aug. 20/1 It isn't just because of rapidly shifting times and attitudes—going back to ‘Lives of a Bengal Lancer’ almost five years afterward, you will find it just as politically incorrect and marvelous as ever.

2000 K. Sewell in J. Thomas Catwomen from Hell 17 This bike of mine was parked outside in the street,..its genuine, politically incorrect crocodile-skin panniers shining with layers of beeswax polish.

PROPAGANDA. (пропаганда). The official party line - slanted information, selectively presented, in an authoritarian regime, which isn't necessarily believed, but people need to accept/"believe". Also, selectively presented news/information strongly favoring one particular political/ideological viewpoint and deliberately encouraging its audience in that direction, e.g: Fox "News", Drudge Report, Breitbart, OAN.)

To go with the original question: in an authoritative regime, opposing the official line is risky. And people - at least those who're relatively well-informed, as opposed to those who have only state-sponsored media as their information source - wouldn't necessarily approve of it, and in fact generally wouldn't.

(Almost by definition, propaganda wouldn't be necessary if the claims made in it were true.)

"Groupthink" is close. The OED defines it as:

A type of thinking engaged in by a group of people deliberating an issue, typically characterized by the making of injudicious decisions through individuals' unwillingness to challenge group consensus.