A book written by Stanley Milgram detailing the implications of a famous experiment of his which has since been outlawed.
The experiment was carried out (roughly) as follows: Subject A is handed a list of words, and told to read designated pairs of words to Subject B, who is situated in an adjacent room. At specific intervals, Subject A quizzes Subject B by reading back one of the words, and asking Subject B to name the word it was paired with. Subject B is strapped into a device which looks remarkably similar to an electric chair, and harnessed down so that he is unable to move. Subject A is separated from him by a wall of glass, and in front of him is an electric box, with a dial and a button on top of it. Each time that Subject B makes a mistake, Subject A is told to press the button, administering an electric shock to Subject B, and then turn the dial up a notch, increasing the voltage that will be applied the next time Subject B errs. The range runs between 15 and 450 volts. Subject A is told that the experiment is being conducted to gauge how well people are able to learn and retain information under fear of physical pain. A man dressed in a lab coat and looking like a genuine scientist stands behind Subject A and marks down results on a clipboard.
What Subject A does not know is that Subject B is actually a trained actor, and is never given any electrical shock at all. However, as Subject A progressively increases the "voltage" being applied to him, Subject B very realistically starts to scream in pain, and complain that he does not want to participate in the experiment anymore. The real purpose behind the experiment is to see to what degree Subject A will act cruelly towards another human in the name of the greater good, Science. As Subject B starts to complain, Subject A will begin to ask the scientist standing behind him if he can stop the experiment, or at least turn the voltage back down. When this happens, the scientist very simply states "The experiment must go on", or tells Subject A that "There will be no permanent tissue damage." He never makes any attempt to physically restrain Subject A, and there is an unlocked door through which Subject A can exit at any time. Most of the time, however, the subject only needs to be told few times that he has no choice before he turns around and begins to administer the experiment again, in spite of the actor's anguished pleas.
At some future date, I'll try and look up some of the figures on how long it took most people to give up and leave, but the point is that the average Joe is quite ready to give up his morals and beliefs about being cruel to other human beings when being commanded even minimally by an authority figure. The experiment was conducted around the time that a number of veteran Nazis were being held on trial for the atrocities they committed in concentration camps during WWII, and somewhat backed up their claims that they were simply following orders, and could not be held personally responsible for the actions of the Nazi Party.
Kevin Smith seems to disagree with this idea; in Clerks, the character Randall tries to convince Dante that position doesn't dictate behavior, and individuals are responsible for their own behavior in all circumstances. Go read the book and watch the movie again, and come to your own conclusions.