The overbreadth doctrine holds that a regulation that curtails protected speech, even if it also restricts unprotected speech, can be challenged as invalid. The doctrine seeks to strike a balance between competing social costs. On the one hand, the threat of enforcement of an overbroad law deters people from engaging in constitutionally protected speech, inhibiting the free exchange of ideas. On the other hand, invalidating a law that in some of its applications is perfectly constitutional — particularly a law directed at conduct so antisocial that it has been made criminal — has obvious harmful effects.