"it's basically indisputable that they are socially harmless."
I wouldn't go that far. Any substance that alters perception, inhibition, etc has the potential for some social impact. For example, public drunkenness, DUI, liquor license etc were created because intoxicated people caused some sort of problem and laws were created around that. While these were created for alcohol, it's likely similar laws would be created for other substances.
My state has no law against public drunkenness and there is no discernible difference here between other states I have lived in which had such a law. Honestly I think that was written as a religious feelzy.
In my state disorderly conduct requires mens rea of disturbing the peace. It's not something you can do accidentally. Compare that to public drunkenness in someplace like California, it's strict liability -- doesn't matter whether you meant to act drunk or not (in fact you can be held accountable for being "unable" to exercise care). They're extremely different laws.
Arizona. It's against the law here to pass a law against public intoxication:
>"No county, municipality or other political subdivision may adopt or enforce any local law, ordinance, resolution or rule having the force of law that includes being a common drunkard or being found in an intoxicated condition as one of the elements of the offense giving rise to criminal or civil penalty or sanctions..."
And in fact they specifically make it illegal to do the thing you suggest, and use other laws as a backdoor against public intox:
>"No county, municipality or other political subdivision may interpret or apply any law of general application to circumvent the provision of subsection A."
(This leaves ability to pass a law at state level, but state has no public drunk law)
They commonly use disorderly conduct against drunk people if they're making a disturbance. You also don't need to do it with the intent to disturb, but just with the knowledge that you are, which is easier to prove.
But my point still stands - there are social negatives that we pass laws around consumption of various drugs (including alcohol), and that they are very similar in most states (AZ might not have a public drunkeness law, but still has plenty about other stuff like DUI, public consumption, age limits, licensing, open container law, etc).
You're oversimplifying. "The law" is not the only thing that dictates peoples' behaviors. There are lots of other reasons why drinking may be more or less bothersome in some states versus others. Different places have different customs, particularly around drinking. Those customs combined with alcohol may create more or less of a public nuisance.
I wouldn't go that far. Any substance that alters perception, inhibition, etc has the potential for some social impact. For example, public drunkenness, DUI, liquor license etc were created because intoxicated people caused some sort of problem and laws were created around that. While these were created for alcohol, it's likely similar laws would be created for other substances.