Ideology is actually an internalized process. They think for themselves, they aren't just mindless fascist zombies, but their ideology makes their thinking take this shape. It would certainly require a lot of unlearning!

Also, their ideology acts as a shield against the trauma of their own actions. Someone who snipes children needs that ideology to survive, because without it they'd likely kill themselves (or frag a superior officer, like sometimes happens when soldiers empathize with civilian victims)