Why did you create “injection clinics” at all?
Junkie culture exists because of heroin, not because it is illegal, junkie culture won’t disappear just because you tell them they can carry it in their pocket now, and buy it at the 7-11.
I don’t know why you think legalizing all drugs and all future drugs, and drug cocktails, and marketing and advertising them and the new drug combos will result in a more “fixed” in place percentage, that will thin itself out through deaths and overdoses.
It’s just the way life works.
The four choices (really three, but for the sake of explaining my thoughts to you...) if heroine is legalized:
(1) Try and at some point, die from it.
(2) Try and not die, remain lifetime addict.
(3) Try, not die, then choose to quit because it is a waste of their life.
(4) Never try it, never die from it, never get addicted to it.
Look at smoking. Many have stopped smoking because it wastes their money, shortens their lives, and makes their life insurance higher. The very same effect will apply to heroine, except heroine is actually less addictive than nicotine.
Plus, if you do your research, even with the illegal use, gigantic police budgets to combat drug use, and all the deaths, in monetary considerations, alcohol is the most expensive drug ever. Opiate users don’t even mildly compare!
Make it legal, and the junky community aspect will fall apart. It won’t be cool any more. It will just be one more thing you can now destroy yourself with legally. Natural social deterrent.
Your nightmare scenario of most of the population of the US becoming heroine users is completely unfounded. Even with the coolness factor among junkies, heroine, while very popular in that community, is nothing as bad as alcohol.