You need to watch this video report:
The report, by Deutche Welle, shows what happens when the government and the police fail to control criminal gangs. The people arm themselves any way they can and fight back. I have often thought that the main reason Mexican gang violence has not spilled across the border is they know Americans are armed to the teeth and will fight back if pushed.
I suspect that the violence will spill over once Mexico completely collapses. Its due. Think civil war.
Of course, the anti-gun crowd would disarm law abiding citizens in America and probably Mexico too, first.