That sounds reasonable, and I personally have no objection to legalizing pot- but that would not solve this problem. The pot smugglers would simply smuggle other drugs. You would have to legalize all drugs and then I imagine they would find something else to smuggle.
Most of the smuggling activity is concentrated in marijuana smuggling because Americans consume more marijuana than all other illegal drugs combined. The ONDCP estimates that Mexican drug trafficking organizations gross $13.8 billion a year selling drugs to Americans, $8.6 billion from marijuana alone. Next in line is cocaine, at about $3.9 billion a year, then meth at about $1 billion a year, and finally heroin at about $400 million a year. If we took marijuana out of the equation, Mexican organized crime would lose about 62% of their gross revenues. It might even be a greater percentage of their net income because they are only the middlemen for cocaine which must be purchased and imported from South America before being smuggled into this country. Taking marijuana out of the picture would take the lion's share of their income from them. They could all try to smuggle in more cocaine and meth and heroin, but there's really a limited market for these drugs. Only a very small percentage of our population want to mess with these other drugs. On top of that, they're going to have a harder time moving these drugs to begin with if we legalize marijuana. The distribution networks for marijuana are huge and spread out everywhere in this country. When Mexican organized crime wants to move some cocaine or meth or heroin, usually they're going to move it through those existing channels. They offer it to mid level pot dealers who in turn offer it to people who are selling pot on the retail level or those who are supplying the retail dealers. All of that is going to fall apart when pot is legalized. They'll be dealing with a lot fewer people who they can tap to move their hard stuff. They'll still have some connections, like gangs they might deal with that sell drugs on street corners or from crack houses, but they're going to lose most all the little part timers selling a little weed to their friends and a lot of the people they buy their supply from. It's going to become harder for them to move the hard stuff. So what I think is more likely to happen is that we'll see a lot of people involved in the business just get out like we saw happen after alcohol Prohibition and those who remain will be killing each other over what's left of the illegal drug business. In the end these drug trafficking organizations will be a lot smaller.