I don't think we have to wait for Mexicans. We have plenty of domestic thugs who are converting to Islam in our prisons, and some of them have indeed gone out and set up shop for AQ when they get out (think of the al Fuqra movement, a black group that has terrorist training camps all over the country, or the terrorists arrested in Seattle and Portland in recent years).
Gang activity makes losers feel powerful. This is the same effect that Islam has on its devotees, because being given permission by their religion to be vicious and have no restraint makes them feel superior to the law-abiding, civilized (and in their view, weak) society around them.
Very well said, Livius. "Gangs make Losers feel powerful" should be on a poster in inner cities.