I don't know if it's all brainwashing. It could also be intimidation and going with the flow as to why people followed him. I couldn't find the exact video of it but it's similar to this (Milgram Study):
Basically, there's three people. One is the learner and the other is the teacher who is under the supervision of the scientist (or authority figure). If the learner gets something wrong, they get shocked as punishment. The shocks intensity goes up over time if they continually get answers wrong. (See where this is going?) Anyways, most people will do as they are told and hurt someone even though no one's pointing a gun to their head and they can walk away.
Back on topic:
This is like a Catch-22. Even though we value society and following the norm, we also value individualism and people who pursue what they like and believe in. But to break away from the pack is a hard road to follow because you can become ostracized, bullied, and who knows what else just for not being like everyone else. It's probably easier to be (and think) like everyone else because then you won't stand out.