TCS Daily

Information Sexternalities

By James D. Miller - April 24, 2003 12:00 AM

Senator Rick Santorum recently compared homosexuality to incest. In a provocative article William Saletan considers "if gay sex is too private to be banned [why can't the same] be said of incest[?]" Avoidable information externalities provide the answer.

An externality is anything that affects parties not involved in the transaction. Factory pollution, for example, is an externality that can harm people who don't own, work for or buy from the factory. Economists believe that externalities often provide a justification for governmental involvement. Externality analysis can be applied to sexual relations.

People deliberately make vague sexual advances for fear of rejection. Rather then blurt out "I'm romantically interested in you, do you feel the same about me?" many of us instead compliment the object of our affections on his or her attire or intelligence. This deliberate vagueness in courting makes it difficult for people to distinguish amorous advances from non-sexual discourse.

Several years ago a student was very upset at having received a D on one of my exams. While she was asking me what she could do to raise her grade she started crying. My first impulse was to hug this young student and tell her everything would be ok. Fortunately, I quickly realize that she might misinterpret a hug, so I didn't touch her. Similar fears of misinterpretation have caused me and many other professors to keep social distance from students and not, for example, ask them to lunch or even praise them too profusely. If professor-student affairs were unthinkable then we would not fear such misinterpretations.

If a woman attends a school in which professors never hit on students she rationally shouldn't interpret a professor's broad smile or gushing compliment as a sign of sexual attraction. In contrast, if she attends an institute in which professors continually pursue students then she should be leery of overly friendly male teachers. Consequently, whenever a professor sleeps with his student he creates externalities for other professors. These externalities force ethical professors to keep their social distance from students to avoid being confused for their Clintonesque like colleagues.

As with professor-student affairs, incest creates informational externalities. Family members are often affectionate with each other. It would be horrible if such affection were suppressed for fear that it would be interpreted as incestuous. In a world in which incest is taboo and rare most people won't interpret a hug from a relative as a sign of sexual interest. Consequently, whenever incest occurs it creates an informational externality that makes it more rational for relatives to misinterpret non-sexual affection for amorous advances. Incest between consenting adults therefore harms society and consequently is not just a private affair.

Homosexuality can also create informational externalities, but these externalities are unavoidable and so do not provide a justification for criminalizing gay sex. Many straight men fear being thought of as gay. One could argue that these men are harmed by the existence of homosexuality, which makes it possible for others to rationally misinterpret their sexual orientation. Criminalizing gay sex, however, would not reduce the number of homosexuals and would thus not decrease the probability of someone thinking any given heterosexual man was gay. In contrast, criminalizing incest would reduce the amount of incest and so would decrease the probability that someone would misinterpret a friendly kiss from a cousin.

To see this, consider an extreme case. Assume that the government is considering passing a law that would impose very significant penalties on gay sex and professor-student affairs. This law will be so effective that it will completely eliminate both activities. Now, assume that some professor fears his friends think him gay and his students think he is trying to sleep with them. The law would do nothing to reduce the probability that his friends think him gay, while it would credibly convince his students that he isn't trying to initiate sex with them.

James D. Miller writes The Game Theorist column for TCS and is the author of Game Theory at Work.

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