Stanley Milgram's Obedience Experiment
After World War II, psychologists and sociologists tried to understand how an entire country of intelligent, civilized people could be ... all » overcome by the violence and hate that prevailed in Nazi thought throughout Germany. Moreover, how is it that someone we would normally identify as a good, moral person could become a merciless mass-executioner.
The Nuremberg and subsequent war-crime trials rejected the defence of "just following orders." Yet Stanley Milgram was able to demonstrate that, if certain conditions are met, a large number of people will do something that they feel is morally wrong when it is an act of obedience to an authority figure.
A large majority of Milgram's test-subjects who believed they were giving increasingly stronger shocks to another person continued to apply those shocks despite the victim's screams and protestations. About 50% of subjects continued with the experiment until all noise and response from the victim had ended, either through unconsciousness or possibly death.
Note the last gentleman's statements where he claims he wanted to stop, but the authority figure would not allow him to, insisting that he go on. The idea that he could simply not do what the authority figure asked doesn't even occur to him. While this experiment is considered grossly unethical by today's standards, it provided valuable insight at the time.