I'm not sure you're grappling with the actual claim parent is making.
Of course for every individual user, it's better to have minor health problems than be thrown in jail.
The question being posed (if I understood correctly) is - if legalization means 10x more people use marijuana, and therefore 10x more people have health problems, is that better or worse than marijuana remaining illegal, and some fraction of the X go to jail.
(Btw this is a false dichotomy, it can be illegal without meaning you go to jail for using, but I digress.)
I would argue that those people will have health problems regardless.
Substance abuse isn't about the "substance" part, it's about the "abuse" part. Naively taking away the substance doesn't address the root cause. The root cause is complex - life sucks, things are hard, and people want to escape.
I'm speculating, but I'd wager higher MJ use means lower alcohol use. On the surface this shouldn't make sense, but it does when you consider the perspective of needing to use something, rather than the something.
Of course for every individual user, it's better to have minor health problems than be thrown in jail.
The question being posed (if I understood correctly) is - if legalization means 10x more people use marijuana, and therefore 10x more people have health problems, is that better or worse than marijuana remaining illegal, and some fraction of the X go to jail.
(Btw this is a false dichotomy, it can be illegal without meaning you go to jail for using, but I digress.)