There's no substitute for the margins you can get in the illegal drug trade. Take away the primary source of funding and you make it much easier to break the gangs. We've already gone through this. Just legalize it already.
Illegal goods have better margins but extortions provide a platform for power and money with less effort.
I would agree that letting black market bs continue will eventually lead to groups that could threaten global control on random other commodities but that's no reason kick the can further down this road.
Finance wars. Like with the "Ten Cents War": https://en.wikipedia.org/wiki/War_of_the_Pacific
No they couldn't. That'd just mint another cartel run black market that they don't control and that cartel would tax the black market coffee at substantially less.
You can kind of think of the current drugs situation as a "so big the number doesn't matter, it's a non stater" percent tax.