It's absolutely true that society isn't really very violent - I don't remember the last time I even saw a fight. But I wouldn't be surprised to hear that prison is rather more violent than society as a whole. You've got young men who tend to be under-educated and under-imaginative, forced into close association with other young men, not given very much opportunity to stimulate their minds. It's more or less inevitable that violence will be part of their lives.
When I'm dictator we will send many fewer people to prison, especially for non-violent crime, and we will actually educate those we do. We will also educate those we sentence in other ways. Why not spend half of your community service doing something practical for society and the other half doing something of more use - discovering your brain?