I keep saying this!!
Nobody uses any substance merely because it's available, people use whatever they use because they have an interest in / desire for that particular drug. I keep getting offered stimulants and psychedelics, I don't take them just because they're THERE. I can purchase cigarettes legally everywhere but I've never been a smoker.
Anti-legalization zealots, in as far as they're even willing to admit this is the only way to cut both drug-related crime and drug-related deaths, will say that to legalize would be insanity because then untold numbers would get hooked and it would be 'a social experiment with uncertain outcome we can't risk'.
I've been in public debates about this and my answer is we're already run the 'experiment'. It was pre-prohibition times. Any respectable person could walk into a pharmacy and buy laudanum, paregoric, morphine, coca in various preparations, hashish paste. Everybody wasn't doing all the drugs and society didn't collapse.
Those who want to use drugs are already doing them, those who have no such affinity won't suddenly run out and smoke crack just because it's no longer punishable. There remains a small cohort of curious but law-abiding individuals, and as far as those are concerned it stands to reason that someone whose want of drugs isn't strong enough to risk the legal consequences in the first place is highly unlikely to become a problem user, even if they become a regular user.
When cannabis was legalized in the Netherlands the hyped-up scenario of a nation of pot-heads failed to materialize. What happened instead was a slight initial increase in customers, most of which, curiosity satisfied, left off again, and the numbers of regular consumers essentially settled back down to what it was.
The proportion of drug users of any given population has historically been quite stable. We have however seen a steady INCREASE of people with addiction problems right in line with prohibition, and the more strictly enforced generally the more problematic use, the more drug overdoses, the more crime. Prohibition not only is a disastrous failure in terms of what it's claiming to want to accomplish but is directly counter-productive.