Why is Doro offended by a lie?

In Octavia Butler’s Wild Seed, there is the following exchange:

"A lie offends me, Anyanwu, and what I see of you is a lie. Show me what you really are."

….

"Can my concealment be a lie if yours is not?" she asked.
"Mine is," he admitted.
"Then show me as you are. Give me the trust that you asking me to give you."
"You have my trust, Anwanyu, but knowing what I am would only frighten you."
"Am I a child then?" she asked angrily. "Are you my mother who must shield me from adult truths?"
He refused to be insulted. "Most of my people are grateful to me from shielding them from my particular truth," he said.
"So you say, I have seen nothing."

Then Doro reveals his truth:

"I kill, Anyanwu. That is how I keep my youth, my strength. I can do only one thing to show you what I am, and that is kill a man and wear his body like a cloth." He breathed deeply. "This is not the body I was born into. It’s not the tenth I’ve worn, nor the hundredth, nor the thousandth. Your gift seems to be a
gentle one. Mine is not."

Why does Doro say ‘a lie offends him’ when his whole appearance is a lie? What does he mean by saying this to Anwanyu?