Jason Kuznicki earns quote of the day honors for this statement; but, you should go read the whole thing:
[T]he state enforcement of private moral conduct almost inevitably produces an even greater moral evil than the conduct we aim to repress. Far from leading to a more moral society, the use of force to police the private conduct of adults achieves just the opposite; in the name of opposing libertinism, the prohibitionists run squarely into something far worse.