I am not sure how legalization will indeed affect overall crime in Mexico. Legalizing Marijuana in the US still won't make it legal to grow it, manufacture it and produce it in Mexico. The main problem is the "tirfecta" between two cartels (Zetas and Sinaloa) and the Government.

I just recently read this article, very interesting for this topic: http://www.economist.com/node/21559598

For what I understand gun control over the border would help crime rates in mexico even more than drug legalization. As a country we're not really big gun manufacturers. And nonetheless, there's an excess of guns in here. So much that there's a program right now where you can excange your weapons for laptops, microwave ovens and similar households. No questions asked, just give the guns away!

Not so much, since heroin, cocaine, and other drugs wouldn't be legalized.

Thanks for the replies! Clearly, a very complex problem.