Well indoctrination is one of those things that's hard to believe unless you see it in action. Its hard to teach about too because it is something that you don't really believe is happening until you've seen it from experience. There are a number of things like that, and to undo the damage you have to have reached a certain level of self awareness which many never get to.

Critical thinking by itself isn't really enough in my opinion either. It only impresses how much additional work is needed, on an ongoing basis, to defend yourself. Its often overwhelming, and rarely are things like negotation and credibility taught in a way that kids can understand.