re: Why is America more violent than comparable countries?

The Western Hemisphere in general has a lot more everyday violence than much of the rest of the world. Even blessed Canada is more violent than all but two of its European counterparts.

In the United States in particular, I think the fact that we are historically a frontier society with a lower regard for the law writ large (as opposed to say, the Netherlands or Germany) plays a significant part. Because of the geographic size of the place and lack of state resources to effectively police this boiling, brawling society for hundreds of years, justice was more often administered in an ad hoc manner than the more formal European methods.

Our demographics play a significant part in it as well: we have almost as many people of Hispanic descent alone in the United States as Italy has people in total. If France or Spain had our size or demographics, I am certain the violence would be different as well.

Can't forget the drug trade, either. That's the biggest driver at the micro-level.