Personally, I think if you call gangs cults, it diminishes the impact of the word. Suddenly, calling WWASPS and other programs cults (which they most definitely are) will not have the same effect, because one could start refering to any group as a cult.
Cult, definitions
* adherents of an exclusive system of religious beliefs and practices
Do gangs fit this description? I'd say no, their practices are similar because they are all of the same socio/economic makeup, they team up to survive and attain things they could attain in no other way than crime.
* In religion and sociology, a cult is a group of people (often a new religious movement) devoted to beliefs and goals which may be contradictory to those held by the majority of society. Its marginal status may come about either due to its novel belief system or due to idiosyncratic practices that cause the surrounding culture to regard it as far outside the mainstream.
The kids in gangs seem obsessed with power, money and shiny metal objects. Sounds a lot like most greedy, capitalistic Americans, doesn't it? They are using the only means necessary to them, trying to reach the same goals everyone else is -- financial and personal security. They are using the only tools available to them, at least the only tools THEY THINK or ARE EASIEST available to them. Why go to college if you can make money as a gangster? Seems stupid to us, but their culture supports this belief. Their goals are our goals. If the goals of gangs were not financial and security related, not ideologically based. I'd argue in fact, underground revolutionary groups at college campuses are more similar to cults than gangs, since it is their common ideology that holds them together, and they wish to work towards a political goal. But I'd still hesitate to call it a cult, if only just to preserve the impact of the word.
I see gangs as the meager simply trying to live like the rich they see drive by in their mercedes everyday. Look at some rap music videos. They aren't about revolution for the underclass and equality, they want to get rich themselves! It's about greed, and violence -- something which our society wants to deny to our lower class, but applauds our elites for the same actions. Strange world we live in.