IMO the key is for so-called "hard drugs" to develop the corrective measures. Arrest them, but instead of throwing a simple user in jail adjudicate them into a treatment program. I've watched two people in my life go from "functional" heroin addicts (as in I couldn't outwardly tell) to missing a week of the drug and breaking into homes to steal. It is not possible to "dabble" in hard drugs like one might have a beer on the weekend or a cigar at a bar. It's 0-100. Watch interviews with former heroin addicts. Chasing the dragon starts from the first hit.
Societal danger should modify the way we treat a drug. Most people agree the solution to alcoholism is not to give alcoholics more alcohol. So too, we should not be giving hard drug users more hard drugs. Treat them.
And I think a big part of legalization is an emergent social aspect. Government legalization of marijuana in Canada has meant that my father has actually had real conversations about the drug instead of just treating it as evil. He's now open to using it for treatment of pain or as a means of 'relaxation'. His peers/friends are also in that group. Nothing about the drugs abilities has changed -- just his perception and ability to speak openly in his social circles.