I agree. Gangs mostly seem to fight over territory...and most of what they want that territory for is selling drugs.
I'd also legalize prostitution. By legalizing these two 'classes', you'd reduce the amount of money most gangs could get from a 'territory' to below minimum wage for the number of gang members they'd need to secure it.
If your criminal enterprise can't produce enough to keep you in bling, it's generally not going to be enough money to justify the risks of jail, prison, and death. So I see that drying up substantially.
Not saying they'll stop fighting, but they'll at least have one less reason to fight for.
Maybe they'll go back to fist fights rather than gunfights? That'd be a bonus.
No one will want drugs from gangsters if they can get clean and safe drugs from the gobmint, even if it's a few dollars more.
Not the government! They'd be commercial, like Bayer heroin. I love picking on Bayer because they hold the patent(expired) for heroin.
And if so many other drugs are available, and Meth is still illegal, then it'd be too much risk and maybe people would decide to go for the lesser, legal drugs.
I'd legalize Meth as well.
It's just that it's dangerous enough I don't see commercial companies getting into producing it, and there are better alternatives.
Plus, with our experience with prohibition, people tended to switch to harder drugs(liquers) over softer forms like wine & beer because liquers were more compact and easier to ship for the dosage level. Legalize the stuff and I see people sticking with cocaine over crack, much less something dangerous like Meth. Those that can't will kill themselves one way or another relatively quickly(and hopefully alone, by stroke rather than car crash).
As an ancillerary, jails/prisons will be free of recreational drugs. None. Want to keep your hits coming? Don't get arrested. Being High wouldn't be an excuse for any crime.