Foul Ole Ron said "the only way to control people is to lie to them", which is pretty much accurate. (Most of what he said in the 1950s was accurate in the sense of being a common-sense psychological or spiritual truism. He even warned his followers "if Scientology turns into a mind-control cult it could screw over the whole planet". The extent to which his practice degenerated to the point where he became what he warned against may be the subject of a later post.) But let's expand that to: the only way to enslave someone is to get them to commit crimes.
That's how cults work. The way you ensare someone is to take away their "self-determinism" - get them to violate their own principles, goals, values and ethical system, on the grounds that the greater glory of The Group justifies whatever means. And at that point they realise that if they ever leave the group, they will have to answer for their crimes in the real world, who will not take "we were only following orders" for an answer. Look at the way that Jack Barnes corrupted and destroyed Barry Sheppard by making him do his dirty work.
I've read an argument - I think it was by Alex Callinicos - that that was the real motivation of the Holocaust. The Nazis knew perfectly well that they were committing the worst crime against humanity ever. But that was how they were going to blackmail the German people into fighting to the bitter end. Note that the mass killings of Jews only happened after Stalingrad. Before then, the purpose of the concentration camps was to degrade the Jews to the point where they actually became the snivelling subhumans that Nazi ideology proclaimed them to be. But the murder machines started up, according to this analysis, so that then the Nazis could turn to their subject populations and say - in the immortal words of Bender B. Rodriguez - "Hey! Guess what you're accessories to!"
Law enforcement know this very well, which is why we have the concept of "turning states' evidence" - we will forgive your crimes if you strike a blow at your former group. But then law enforcement's goal is to shut down criminals and groups of criminals. When you're dealing with other groups of people who have a highly developed sense of "right and wrong", or are crusading against something as unreal as an idea, they will tend to turn on renegades from their enemy because at least that's something they can punish. As Marty Rathbun is sadly finding out. Anti-Scientologists are (a) disinclined to forgive him for the crimes he committed due to his former allegiance to a psychopathic leadership; (b) against the idea of Scientology rather than the crimes committed in its name.