My spouse, a criminal defense attorney, used to be a pro-legalization liberatarian type, but is now not so sure after working in the system.

Pot isn't a big deal, but the problem is with drugs like meth, which are both much more ddictive and much more rapidly destructive than tobacco. Make meth widely and legally available and unless you're really willing to not just "lose" in the abstract a significant fraction of your population, but to basically just shoot them once they're messed up, you have a problem.

If you just try to ignore all the addicts, you end up paying huge, huge health care costs caring for them after they've damaged themselves so badly (and this damage kicking in while they could still be a productive young adult, not as liver or lung disease in their 60s).

Meth, unfortunately, tends to increase the unintended pregnancy rate a lot because, though this isn't advertised much by the drug policy people, it apparently really does make sex mind-blowingly fantastically good while you are high, and makes you hornier than a crazed weasel too. So even if you don't care about the meth head, you still have the meth head's neglected (and probably drug-affected during pregnancy) kids that society has to take care of, unless you start making Soylent Baby out of them. Raising the disabled kids of drug addicts is a pretty big slice of the social services budget in most places, and making the drugs legal doesn't mean the kids aren't neglected or sick anymore.

Second, you don't solve the crime problem. Instead of Greedo the Street Dealer getting his meth from an illegal lab or Mexican traffickers, he gets it by walking into a high street store and buying it. Then Joe the Addict still holds up the local gas station or steals his neighbor's TV for cash to hand to Greedo for a hit of meth. Or Joe just walks into the high street shop, but I figure there they might be suspicious of selling to a disheveled, spaced out guy whom the police might well be looking for.

If you take a harsh, "evolution in action" approach and you do just put the addicts -- and their kids -- on a melting ice floe when they need medical care and impose capital punishment for committing robbery to support a drug habit, then legalization works. Short of that, for the really hard drugs it's problematic.

That being said, we probably could legalize pot without a big problem, and the particular ways we fight the drug war in the US are far more expensive and destructive of civil liberties than they would have to be to get the limited results we get.