The cartels aren’t drug evangelists, they’re businesses. Take away drugs and they’ll violently monopolize other profitable export industries. In fact, they’ve already done this with avocados.
If you want to stop the violence and corruption of the cartels, you’ll have to either change the culture that makes their existence possible, or defeat/imprison/kill them all. I’m not sure which of those would be more difficult.
There are no other criminal enterprises that offer a comparable revenue source. Not one. It's utter nonsense to think that organized crime is just going to switch to avocado extortion and keep bribing their way out of jail.
The Sicilian Mafia has gone mostly “legit,” in the sense that they operate in legal industries, e.g. olive oil. They just use criminal means to extract hugely excessive rents from those industries.
They aren't competitive internationally, though. And can't be unless they're also going to go down to Morocco, fight the Army, invade Tunisia and Algeria, and then force the extraction of high rents.
Human trafficking and gun running are the cartel’s other significant sources of revenue. Then there are extortion and protection rackets. You could legalize absolutely everything and you would still have cartels. In Africa they are run by warlords and drug smuggling isn’t a big thing there — anywhere you have poor people and a weak government, you’ll have some form of “cartel.” The product is irrelevant.
If they could violently monopolize some other industry, why aren't they already doing so?
I would assume they are already trying to expand as much as possible. Legalising drugs doesn't look like it would make that expansion easier. If anything, it would become harder, because funding dries up, so investments are harder to make.
If true then what is a workable solution? Does Mexico need UN peacekeepers to reinforce the government's efforts to retake control from cartels and corrupt militaries?
How sustainable is any change if people believe criminals will just regain power once help leaves?
If you want to stop the violence and corruption of the cartels, you’ll have to either change the culture that makes their existence possible, or defeat/imprison/kill them all. I’m not sure which of those would be more difficult.