Mock the truth that they fear and make it seem as if only a paranoid idiot would believe it. Make their truth a straw man, and knock it down.
What he should have thought to defend his mind: I'm as normal and healthy as any one of the azi she redesigns.
You can't implant commands that don't work off something, some buried or halfaware thing, that isn't already there. You can work in a series, and find that first hook, and hook something off that, and keep building until you have a long snaky trigger you can tweak.
If I understand my whole mind, what will be lurking in the part of my mind where my eyes don't go, laughing at me? If I understand all my motivations and quirks and weaknesses, will my mind collapse like a house of cards (trite, overused phrase, that) and what will be born of the rubble?
I fear my sexual desires. I fear sharing my desires. I feel I'm too kinky for my own good, and sometimes swear off some things, only to go back to them. Could I handle a husband who won't do some of those things I desire? If I ever have a partner who won't let me masturbate, that's a dealbreaker right there. I know it's prudish, the things I fear and enjoy, and I hear about things I'd never dream of, and I celebrate it in others, but as for admitting it of myself... Biology.
I fear what will happen once I know myself. Will I hate myself? Will I destroy my own mind in a puff of vengeance? I am my own worst enemy. Right now I feel I need some external force to control me against myself, and I think I've chosen well, the one person who makes me a self that I like.