The Banality of Evil
Week 3 of Coursera Social Psychology course deals extensively with three famous sets of experiments:
1) Milgram experiments on obedience to authority figures
As all these experiments are quite famous (refer to wikipedia links) I would not go into any detail here. Even though I had knowledge of all these experiments before, it was quite chilling and insightful to see the video recordings of the original experiments (the lecture materials included Obedience, Milgram's documentary on his experiments, and Quiet Rage, documentary by Zimbardo).
The take-home message, so to speak, is the immense power the situational factors have on our behaviors, something that we are, in general, blind to. Under certain circumstances, people will continue to obey orders, despite reluctance, that they can apprehend to be morally objectionable, if the orders come from an authority figure. Under certain circumstances, people will conform with the group opinion and behavior, even if it means contradicting something one knows to be obviously correct. Under certain circumstances, when people in positions of authority become deindividuated, they will easily slip into a mindset in which they subject others to degrading, brutal and inhumane conduct.
This vulnerability lurks within all of us.