And the interesting thing is, all of that violence is directly related to overly harsh laws relating to narcotics. The problem comes down to economics:
There is an immense demand for narcotics. Since narcotics are illegal, they are risky to trade, which pushes up prices. Through a combination of the preceding two points, trading in narcotics is extremely profitable. Since the different trade groups engaging in the trade of narcotics have no legal means through which they can resolve their differences, they will instead turn to violence.
The gang member's real offense is being born in a crappy part of town lacking in institutions and resources, and where engaging in the drug trade is a normative experience and one of the few sources of jobs. That at least The Wire really goes on about.
By eliminating mandatory sentencing, you will significantly reduce the amount of years people serve in prisons because the mandatory sentence lengths were established capriciously in an attempt to out grandstand political opponents (see http://www.thisamericanlife.org/radio-archives/episode/143/s... ).
The world isn't quite as black and white. Eliminate the War on Drugs and overnight all of these problems will disappear as the underlying incentives vanish.