I'm not for barring people from forming clubs or organizing but I am for members of said clubs to be responsible for controlling the actions of their clubs.
That being said, if your club is known for committing violent crimes, the club should be forcefully disbanned. Preferably by deadly force. Special police forces paid for by filming and made available on pay-per-view during their exercises.
That would solve a lot of the urban crime. Wipe out a portion of the element, make joining gangs VERY dangerous from the lawful side, confiscate a pelethora of guns, and funded by people sick enough of gang intimidation that they are willing to pay to see gang extermination in action.