In the years immediately following the Holocaust, studies tended to associate the horrendous genocidal acts with pathological personalities. This was understandable as it reflected a common social need: If one could attribute the Holocaust to specific bad or insane types of people, the future might seem different. All that was then necessary was to screen out the potential killers and prevent them from completing such evil acts, and the world would become a safe place once again. It took a great deal of human insight from philosophers such as Hannah Arendt and research by social psychologists such as Stanley Milgram and Phillip G. Zimbardo to understand the so-called banality of evil: that for the most part normal people, sometimes even well-educated people, carried out the industrialized killing of the Jews, Romani, Jehovah's Witnesses, and mentally ill in Nazi Germany. These findings were especially disturbing, as they suggested the...