Legalizing drug possession in Mexico will probably increase the illegal drug business activity north of the border as well, unfortunately.
Personally, I've long thought that legalizing and taxing/regulating many "recreational" substances across the US would be a relatively good idea. Much like the prohibition of alcohol served only to finance the business of illegal organizations, the illegal drug trade produces far more damage to our society than if the same wares were available to interested parties from licenced vendors. Across the nation gangs would be out of business overnight, and the cost of incarcerating ever more offenders in the trade would be quite a reduction in the tax burden to all of us.
There would be an increase in addictions and DUI problems, of course, but isn't there plenty of such evils from alcohol abuse already? I think the increase would be the lesser of two evils... what WOULD diminish is the robbery, murder, etc. of innocent victims in order to finance one's habbit, and the slaughter of eyewitnesses to the crimes related to illegal drug traffic. Even homeless winos can panhandle enough to maintain their daily habbit, so too would those addicted to other substances if they were available legally with the competition based pricing that would ensue.
I don't know about anyone else, but if this were to pass I for one would certainly not suddenly become a cocaine or heroin addict simply because it was readily available. I'm no alcoholic, either even though it's sitting there waiting for me anytime.