Several times a year I work in San Francisco from around 7 PM until 2 or 3 AM and I have only once seen a violent crime in the process of going down. It was an attempted rape right there on United Nations Plaza (Oh! The irony!). I was with my crew of three men, we went over with some metal pipes and put a stop to it. Unfortunately that was all we could do and the guy got away. But at lease we put a stop to it.
Point being, not all big cities are as violent. Granted, mine is but the experience of one guy, and I have seen plenty of drug use and even had a guy ask me if I wanted to buy some crack (I told him to get the fugg out of my face before I got out of my truck and beat him to death- he apologized and left as I started to open the door.) There is more deviant behavior than I can begin to describe, but not a lot of violence.