The big mistake you're making is that legalising it also magically brings all the infrastructure to neuter the cartels.
The problem the cartels will face is that there is no other business that makes as much money, and it would require a retool of the entire organization (or scale up, at a minimum) to get back to even a fraction of their power.
Cartels are not some unstoppable juggernaut: they run on capital, same as every other business. No money for bribes & no money for foot soldiers == no more cartel at a recognizable scale.
This is not true. See this article[1] and HN thread[2]:
> “It’s good business,” El Polkas says with a shrug. “It makes a lot of money.” When I ask how gasoline compares to narcotics, in terms of overall revenue to Los Zetas, he rubs his index fingers together. “Fifty-fifty,” he says. “It’s approximately as profitable as drugs.”
[1] - https://www.rollingstone.com/culture/culture-features/drug-w...
And a quick search reveals:
>he Mexican government said fuel theft — huachicol as it is known in Spanish — decreased from about 60,000 barrels per day in 2018 to about 11,000 a day in 2019, with estimated savings of $6 billion.
> According to Pemex, fuel theft averaged about 4,440 barrels per day in 2020.
https://www.freightwaves.com/news/despite-some-successes-mex...
I have no idea how good the source is, but there's just absolutely no way black market fuel sales could ever generate the same amount of revenue.
> On 2 July state-owned oil firm Pemex reported a 114 per cent year-on-year increase in illegal tapping during the first four months of 2020, during which authorities recovered 9,291,986 litres of stolen fuel with a commercial value of MXN157m (around US$7m).
10,000,000 only has a commercial value of $7m. Imagine the logistics of scaling that kind of operation.