#1 is huge and compounded with the caveat in your asterisk could be even bigger. We can’t predict how behaviors and supplies would adapt. There would still be an illegal drug trade across the border. Untaxed and unregulated is cheaper. That some problems may be lessened isn’t terribly compelling.
Agreed on all counts, except it’s hard to say about the illegal border trade. Certainly there’s an illegal trade in untaxed/unregulated alcohol across the border right now, and if the cross border drug trade reaches those same levels, I’m not sure that’s very relevant.
I would challenge #4. I see no reason not to treat it like a public health concern now, when mere use could be used to compel rehab. That would be much smarter than sending someone to prison in many cases. Treating something as a public health concern doesn’t mean there is a great rate of voluntary treatment.
There are tons of drug users who never even get a side-eye from the police, let alone jail time. Since alcohol prohibition ended, we have lots of recovery programs for alcoholics that appeal to your boardroom executive and soccer mom. During Prohibition, people would stay away for fear of admitting being involved in something illegal. That said, I agree there’s no reason not to treat it like a public health concern now. It’s just that your boardroom executive and soccer mom will very likely opt out of anything that may compromise their standing.