With Mercedes releasing the first mass-produced self-driving car this year, it will probably be only another fifteen years or so before technology will have eliminated the threat of impaired driving. Overall criminality is surely increased by the criminalization of drugs, but suppose people have varying degrees of anti-social propensity. Is the anti-socialness of the general population decreased when we incarcerate drug offenders? Maybe, but on the other hand people are probably a lot more anti-social after prison than they are when they go in, so the effect may run the other way. And anyway, locking up drug users because they might be slightly more inclined toward other bad behavior is an inefficient (and spooky) way to improve society!

And boy would legalization reduce gun violence!