I think all drugs should be legal because it would allow for people to get whatever they want through a legal path rather than an illegal one.
In this hypothetical legal system, it should be required to take classes and exams like people have for driving. Where I'm from, I had to take a short quiz for a learner's permit and then go through a 6-hour exam on driving safety before I was allowed to take a physical driver's test for a license. Despite these requisites, many people are able pass them all and still suck at driving, to the point where they hurt others all the time (texting, drinking, inattention while driving, etc.).
That said, I think the approach should be similar with hard drugs like heroin, cocaine, ketamine, mdma, etc. If you can learn about all the statistics, side effects, death rates, etc. in a 6-hour class AND you still want to use that drug, then that is your prerogative as long as you're 18 or older.
I do think that the first few times, minimum, should only be allowed under direct medical supervision under licensed medical practitioners until they are deemed fit for private use within the home. If you get caught using in public places (e.g. in front of kids) you should be fined, sent to rehab, prohibited from purchasing any more of the drug legally, or whatever punishments are deemed appropriate for their situation. If the bad behavior continues, prison seems to be the only option left, so the idiot could sit there and think about what they've done.
However, this all seems to be a utopian pipe dream. All I can hope for is the opportunity to find drugs like psilocybin, LSD, and DMT through legal means rather than the black market for use in the home or (at minimum) under medical supervision.
For now, I think cannabis should be legal just like tobacco and alcohol are. They seem to be far worse in terms of bodily harm, so I don't see why I shouldn't be able to grow a plant and use it for recreational or medical purposes.