I think you have good points....but thinking of a family member with decades of substance abuse--drugs and alcohol--I cannot figure out how legalization would have helped him. I really wish that I did. I came the the realization several years ago that I had probably never seen him not high on something. He was really good at presenting himself well. It is only in retrospect that I realize that he was probably altered that time.... Now: his brain is not great. And his emotional development stopped at about age 15 or so. He still makes important decisions like a 15 year old boy in the throes of adolescence. And yes, the volatility is there. He claims he's not using but then he will mention the pain meds he's on for this or that: I do NOT disagree that he needs relief from pain and will throughout his life. He's always managed to work so generally, his habit was covered. However, there were times when he did steal from family members and doubtless told himself that they could afford to lose whatever it was that he took. This was not actually true. Would it have been better for him if his drugs of choice (and it changed over time, as is often the case) had been legal? Maybe. It would not have helped him be sober enough to be a decent human being, to not be abusive to those around him, to be reliable, to parent. All of those things have caused a great deal of heartache in the family. Not to mention lots of money.
I'm also thinking of a young adult who grew up spending a lot of time in my home. Their parents abused alcohol and one also had a gambling addiction. The parents were two of the most talented people I knew--extremely artistic and the father was also a very gifted craftsman. But the alcohol abuse dramatically affected their ability to perform on jobs. There was tremendous economic insecurity, and that was with grandparents helping out substantially. As for the kid who spent so much time at my house: they're struggling a bit with their own alcohol abuse and also caught in a custody battle and the serious health issues of their father (stage 4 cancer...). I don't know much about the dad's family but I know that the mother was raised in a very middle class and very loving and supportive family. All of her siblings have struggled with some degree of substance abuse except one, and I believe that's why that sister divorced her ex.
I've mentioned before that I live in a small town. The local newspaper will publish if the fire department comes to your house for a cooking fire generating smoke. So, it's pretty easy to see why people in this town are arrested. Almost 100%, either drugs or alcohol are involved. Occasionally both. My son is a public defender, serving mostly residents in a county that is even more rural than mine. Almost every single one of his cases involves drugs. He's for legalization. We've talked about why the current generation of young 20 somethings would ever touch the stuff, seeing how it destroyed their parents and maybe grandparents. His opinion is that they do it because in their experience, that's just how you coped with bad stuff: pain, job loss, break ups, fights, etc. Of course that's all a very vicious cycle as using drugs to cope with emotional needs causes more pain, job loss, break ups, fights, all kinds of instability. Rinse/repeat. I don't see how legalization would stop that or even slow it down.
Unless we used that money to actually treat mental health issues. I don't see that happening, although there is desperate need.
So, that's why I'm hesitant. Legalization will make it more easily available and so more used.
I'm also a bit hesitant because for a lot of addicts, they seem drawn to the next bigger high. Which involves things like bath salts, more damaging stuff. Starting in your teens or twenties and using for a lot of years really increases the likelihood of increased usage and of more toxic stuff.
I think that pain management is one issue. The other issue is that it is my strong belief that many people abuse various substances because of untreated mental health issues and also because of despair.