One of the principal themes in the debate about drug legalization stems from libertarian thinking: That it's up to the individual, not the state, to determine what a person puts into his own body. Drugs, from this point of view, are a "victimless crime."
Only they aren't.
In the real world, there are simply too many people who are too immature, uniformed, addiction-prone (or addicted) or just too clueless to allow legalized drug sales. There is a legitimate debate going on about whether marijuana is sufficiently dangerous to remain criminalized -- although it's "criminalized" mostly just in theory (visit any college campus) -- but the broad-brush "victimless crime" theory of drugs rests on a blinkered view of the enormous amount of damage and misery drugs cause.
I'll freely concede that, for reducing drug harms, a better culture is to be preferred to law enforcement. But until we get a better culture, it is, in my view, indecent to relax the present legal prohibitions on the recreational use of dangerous drugs, knowing how many people they will damage or kill.