Robert P. George, natural law theorist extraordinaire, is in my morning paper:
Considered as isolated acts, someone's recreational use of narcotics, for example, may affect the public weal negligibly, if at all. But an epidemic of drug abuse, though constituted by private acts of drug-taking, damages the common good in myriad ways. This does not by itself settle the question whether drug prohibition is a prudent or effective policy. It does, however, undermine the belief that the recreational use of drugs is a matter of purely private choice.
A lot of my conservative friends are fans of George, I think, and look to him when making arguments against gay marriage. (He's talking about pornography in the current column, though.)
What's striking, though, is how closely this argument for drug prohibition mirrors the argument for, say, banning old-style lightbulbs in favor of more energy-efficient modern models — a project that caused no shortage of chest-beating among many of the same conservatives who are allied with George on matters of morality. It's an odd concept of liberty and governent's proper role in our lives that anguishes over lost light-bulbs but feels free to deny the marriage contract to individuals.