They'd have the capacity for a moment, but they'd have lost their primary source of income. Human trafficking and extortion don't come anywhere near the risk/reward ratio or volume of drugs.

Some of the cartels would go legit to become drug companies. The ones who wanted to remain criminals would have to downsize their organizations to fit the remaining markets.

Where is this meme originating? It a lame argument that ignores the problem in every way. It pops up so often I want to know where it's being broadcast from.

Yeah, just like the Italian mafia was around long after the US repealed alcohol prohibition. That doesn't mean the repeal was a bad idea, or that it didn't help in combating organized crime.