I think most of us would agree that all drugs (drug use) should be decriminalized. But even if you go as far as to imagine the Mexican cartels being (eventually) legitimate businesses, the strong competition between them would not subside, so they would still fight each other and keep their grip on the government and the population. (Then there's also the ties they have to the governments of the target markets, and their policy making.)

I think to solve this situation, you'd have to diminish the demand for their product in the target markets, which is next to impossible due to the addictive nature of the product. One way to do this would be to legalize and promote therapeutic use of drugs which are known (among many other positives) to break drug addiction (in just a few sessions), like psilocybin mushrooms or Ayahuasca.