Gang violence makes up most of the violent crime that happens in the United States - http://en.wikipedia.org/wiki/Gangs_in_the_United_States#Gang... - 48% in most jurisdictions and 90% in others. Who ends up in gangs? Children who grow up in broken neighborhoods and families http://www.ojjdp.gov/jjbulletin/9808/why.html

I doubt that most people who commit violent crimes were violent people from birth. Most of them were probably forced into a lifestyle in which it is the norm. This is not to say that these people aren't accountable for their actions, but we should definitely understand that most of these people grew up in circumstances where violence was unavoidable and that instead of punishing them indiscriminately, we should try to actually 'correct' them in correctional facilities by healing them and trying to help them become functioning, productive members of society.