It's called duty. They don't have to be brainwashed technically, just believe that the Empire is the better choice for the galaxy than the Republic. They put up with psycho sith because they feel that if they take of the galaxy it will be better. It's completely just a point of view thing. As for the IAs. It's their duty to take the **** they do. But I mean, they are the not-so-secret police. It's and easy thing to flaunt over every non-sith. You just have to think of people raised in a society where you do NOT defy the upper class. Oh wait, that's happened on our planet and in our time as well.