i live here, and don't much worry about gangsters bumping each other off. Unlike the gangs in the U.S., folks here normally don't take out innocent bystanders. But, the feeling in Mexico is that the problem is caused by the U.S. (yeah, I know... Mexicans blame EVERYTHING on the U.S. -- and some folks here blame everything on Mexicans so it's a fair trade). There's more than some truth to the matter. Drugs are one export the U.S. isn't trying to regulate off the market (unlike fruits and vegetables, but that's another thread)... the U.S. is the world's largest consumer of these products (50% of the world's narcotics are consumed in the U.S., according to the CIA's world fact book).
The Mexican response is to blame the violence on the U.S. drug consumers. Hey, most here want capitalism... this is just the ugly side of it.
I don't say the US demand doesn't drive the market--only that the corruption in Mexico allows various gangs to flourish with a quasi-legal franchise that is revoked from time to time as pressure is applied from the US to show the government is responding.
This theory isn't an original thought of mine; it comes from a very informed and astute Mexican intellectual and was published widely a few years ago.