Should we criminalize chocolate bars and hamburgers as well then?
This argument always sounds like a fallacy to me, as we're talking about legalizing something that was previously not, not the other way around.
I get that the argument might be seen as relativizing by providing examples of legal substances everybody agree today should be legal, but the way this answer (and others) is always presented sounds to me excessively aggressive and non-productive. If you want to make a point, please make it, don't just stop at this absurd proposition.
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Some people (I'm not even included in that group as I don't really care about this issue) seem very concerned about the global health implications of cannabis legalization.
Instead of aggressively diminishing this opinion with whataboutisms, legalizing proponents motivated enough to answer to this person should IMO better take into consideration (and respect) this opinion.
It's called assuming the consequent.
Regarding the US: We already experimented with alcohol prohibition. It failed for the same reasons that marijuana prohibition failed. (I believe Europe did the same thing, but I'm less familiar with its history.)
You're advocating for a "nanny state" law. These are difficult in democracies.
In the US, we see debates about similar issues: Some people want to ban guns, some people want to ban abortion, some people want to ban bad drivers, some people want to require helmets for XXX.
Nanny state laws only pass in the US when the politicians who pass them know they will get re-elected. (IE, the US has some areas with very restrictive alcohol laws, because the people in that area believe drinking is a sin.)