Sex is dangerous. Sex puts emotional and physical health at risk, sometimes with fatal consequences. Sex is potentially addictive. Even for nonaddicts sex is repeatedly “Past reason hunted,” and after a successful chase, “Past reason hated.” Teens are particularly vulnerable to sex-related dangers. Third parties suffer from the sex (or the search for sex) of others, through noise and violence and public health care costs. In terms of each of the 3⅓ standard vice concerns – kids, addicts, externalities, and harms to nonaddicted adult participants – sex fares poorly. Surely, if a new drug emerged with the same vice profile as sex, legislators would rush to ban it.

But sex is popular, and so it remains legal for adults. Those types of sex that are less popular – homosexual relations, incest, bestiality – regularly are illegal. Commercial forms of sex, including prostitution, pornography, and exotic dancing, tend to be banned or strictly regulated, even in societies with relatively liberal rules governing sex.

The main focus of this chapter is the application of the robustness principle to the regulation of pornography and prostitution. Before looking at commercial sex, however, I note a few sexual issues involving kids and addicts, followed by an examination of sadomasochism, a variety of sex that underscores the potential for harms to befall nonaddicted adults.

KIDS

Teens and young adults seem to be more at risk than their elders for suffering undesirable consequences from sex. In the United States, infection rates for sexually transmitted diseases tend to be much higher for older teenagers and young adults than for their elders; nearly half of new HIV infections develop in the 15 to 24 age group.