> I’d expect cartels to welcome the change as they can do away with fighting the law (where they no doubt pour a lot of their resources into) and start operating as legitimate businesses.

Prohibition reduces competition which raises margins. It's the same reason why large corporations like regulation that destroys small competitors. The cartels don't want to have to compete with Joe Farmer in Iowa growing drug crops and selling them at the same margins as corn producers do.

If drugs were legal I imagine that other than the cartels would produce and sell the drugs. Maybe big pharma and the tobacco industry.

Your definitions of cartels & force are different to mine :)

Legitimate opiate producers compete in the same market with illegitimate ones. The force they use is police, dea, etc., instead of guns directly, but the techniques are the same.

After all, a state is what happens when organized crime expands its time horizons.

they won't function as legitimate businesses. there's not significant money to be made growing legal crops or synthesizing simple, 100 year old compounds. their business is operating a supply chain that most nation states are busy trying to disrupt.