Hard not to take Roy's side on this one. Seriously, what good can come from being in a gang besides being 'protected' from other gangs?
It's not like gangs are not for profit organizations or affiliated with anything positive in particular. The mere involvement with a gang is bad, regardless of whether or not a particular member is doing anything illegal.
It all starts from a young age and making sure young people have options outside of joining a gang is probably the best way to address the issue. Making gangs illegal is a close #2, though. TP to Roy.