In the year 1971, Zimbardo accepted a tenured position as professor of psychology at Stanford University. There he conducted the infamous Stanford prison experiment, in which 24 normal college students were randomly assigned to be "prisoners" or "guards" in a mock prison located in the basement of the psychology building at Stanford (three additional college students were selected as alternates, but did not participate in the experiment).
The students quickly began acting out their roles, with "guards" becoming sadistic and "prisoners" showing extreme passivity and depression. Prisoners and guards rapidly adapted to their roles, stepping beyond the boundaries of what had been predicted and leading to dangerous and psychologically damaging situations. One-third of the guards were judged to have exhibited "genuine" sadistic tendencies, while many prisoners were emotionally traumatized and two had to be removed from the experiment early.
The bottomline is that Good Apples can turn Bad in Bad Barrels. Therefore before we blame individuals, the charitable thing to do is to first find out what situations they were in that might have provoked this evil behavior. Why not assume that these are good apples in a bad barrel, rather than bad apples in a good barrel?