Rapists and Abusers

I've been reading various discussions about the gang-rape of a 15-year-old girl in California and the aftermath. One constant, as with almost every such conversation, has been the mindset when it comes to rapists and abusers.

There's a strong sense of us vs. them.  How could they do this? How could the bystanders just watch? I've come across various theories–they were poor and desperate, they were in a gang, they were drunk…

We want our villains to be easy to identify, like on TV.  We...