Hitler came to power in a democratic way. The Germans loved him and sacrificed their lives for him. They never woke up from their delusions. They never realized that they were mad until they were defeated.
Nazism is proof enough that a belief system can be incredibly powerful and incredibly idiotic. Almost all people understand today that Nazism was madness and that madness is not necessarily something in our true nature. Beliefs can turn us into idiots. We are not born idiots.