When the “enemy” is different, an outsider, it’s easier to draw quick conclusions, to develop stereotypes. It’s simply human nature: There is “us,” and there is “them.” But what happens when the enemy looks like us — from the same tradition and belief system?

That is the conundrum in the case of Norway and Anders Behring Brevik, who is being called a “Christian extremist” or “Christian terrorist.”

As westerners wrestle with such characterizations of the Oslo mass murder suspect, the question arises: Nearly a decade after 9/11 created a widespread suspicion of Muslims based on the actions of a fanatical few, is this what it’s like to walk a mile in the shoes of stereotype?

Psychologists say stereotypes come from a deeply human impulse to categorize other people, usually into groups of “us” and “them.”

“Sadly, the last ten years, the term has been co-opted in public discourse and only applies to Muslims,” he said. “Now here we have a right-wing Christian extremist who has committed an act of terror, and many people don’t know how to react.”