David Berreby discusses ongoing research:
In contrast to how we perceive them, the majority of terrorists, insurgents, and perpetrators of mass killing who have been tested by scientists have proven to be basically like the rest of us. That’s not to say that participating in a genocide or blowing oneself up in a crowded market is normal, but such behavior is not evidence of personality disorder or other serious psychopathology; rather, it’s an adaptive state of mind that mentally healthy people are entirely capable of adopting. In the case of Islamist terrorist groups, Atran says, “most foreign volunteers and supporters fall within the mid-ranges of what social scientists call the normal distribution of attributes like empathy, compassion, idealism, and wanting to help rather than hurt other people.” It’s proof of what the mid-20th-century political theorist Hannah Arendt famously called “the banality of evil” in her consideration of the seeming ordinariness of Nazis who committed atrocities in World War II.
“Ours is a ‘banality of evil’ approach,” says Hammad Sheikh, a psychologist at the New School for Social Research and collaborator with Atran and Wilson. Sheikh’s personal interest in the psychological origins of group violence began when he was growing up in Germany. “I could never believe that the Nazis were these evil people who had taken over. Millions of ordinary people had followed Hitler, and I met them. They had been fanatics. But in my childhood, they were nice old people shaking my hand and giving me chocolate.”