Thing is, loony dictators like Turkmenbashi, Idi Amin, Caligula, Mao, or Hitler don’t take power as total loons. They achieve total loondom only after they acheive total power. Sure, they may show signs of looniness, ranting and raving about the Jews or Isis, or whatever. But it’s not obvious to their supporters that to put this guy into power means he’s going to deify his sister or have his enemies cooked and served for state dinners.
See, you have to work up to that. You have years where any questioning of the dictator means swift and merciless death, or long and merciless death. You have years where the dictator builds up his security forces, so you never know who you can trust. Sure, you’ve known Mustafa since you were kids, but if the secret police have his wife and daughter in a torture chamber there’s no telling what he’ll say or do.
Saddam Hussein used to require military officers to casually ask their buddies about forming a coup. If the buddies didn’t immediately report the conversation–which, if legit, would mean the death of the instigator–they were immediately rounded up shot in the back of the head by the secret police. So when someone approaches you and starts talking about what a loon Saddam Hussein has been lately, you never know what motivation this person has. Are they trying to trick you into a making statements against the leader? Statements that could mean the death of you and your entire extended family? Safest thing is to assume all such people are provacteurs working for security, and to report the treason immediately.
So when you get to the stage where the dictator is going off the rails, no individual person can do anything to stop it, and anti-dictator organizations are almost impossible to form. The security forces by this time are full of people who just like to torture and murder, they couldn’t care less who they torture or why. So the only effective people who can plot against the dictator are those at the highest levels of government/military, or the dictators personal security foirces, or the dictators household staff. Which is why you get things like Stalin’s “Doctor’s Purge”. He was convinced his doctor was conspiring against him, so he ordered doctors in general to be rounded up and sent to the gulags/execution.
And the security forces round the people up and shoot them and torture them because it’s fun for them, or they think if they don’t carry out the purges they’ll be purged themselves, and there’s nothing they can do for the poor bastards they have to execute, if I wasn’t doing it someone else would, and the only difference is that me and my family would be on the list now. So everyone cooperates because the alternative is death, and when death actually comes for you it’s too late.