But there are plenty of things that are illegal and for which people get charged which lack a deep moral transgression, like drug use and/or dealing, prostitution, illegal gambling. This is one of those things. Personally, I think Craig's hypocrisy is quite enough, so that one does not need to dwell on his "abnormality". So long as there are public restrooms, gays will have sex in them on occasion. Just like prostitution will always be with us. (BTW, I believe that prostitution and recreational drugs should be legalized, but not sex in public restrooms. But then, I'm not gay. ;-) )

As for the evolutionary biology angle, evolutionary biology is not like economics: it doesn't suppose that people are "rational". Women are designed to get pregnant, and by men with the best genes they can get. Therefore, they will on occasion engage in risky behavior if they are sufficiently attracted to someone. (They are designed to be predisposed to have sex with someone who is likely to have good genes, whereas men are predisposed to have sex with anyone, especially if she is fertile.)

When I was speaking of evolutionary biology applied to human sexuality, I was thinking of Donald Symons' work. Here is what I got by Googling:

Since young mammals develop in their mother's bodies and require nursing, mammalian females have few offspring and must insure the survival of each. Therefore, females tend not to be promiscuous. They approach sex cautiously, only mating with superior males. For the human species, male superiority is expressed in power and wealth as these contribute to a child's survival. For the vast majority of animal species, the young are produced by almost all the females mating with a much smaller group of superior males. For humans, polygyny has been the norm for most human societies.

Unlike females, males of almost all species can reproduce with little or no investment beyond the sex act itself. Therefore, males are promiscuous, seeking immediate sex with willing, or even unwilling, females (rape). They compete with other males for females and have a large body size adaptive for fighting. For the human male, warfare, killing, control of territory and resources, are important means of securing females. These behaviors have a strong biological basis. The command of Moses in Numbers 31:17 to kill everyone but the virgins makes good genetic sense. Men don't seek women of power and wealth. They seek women who are young, healthy, and fertile, since a healthy uterus and the ability to nurse and care for offspring are critical for a child's survival.

Since men and women pursue different sexual strategies, heterosexual relations are always a matter of compromise. For homosexuals, however, sexual strategies coincide and "the sexual activities of homosexuals of both sexes appear to be especially intense, varied, and satisfying." (Symons, p. 298). Further, since strategies coincide, female homosexuality reveals how females in general approach sex, male homosexuality the male approach. Lesbians have few sexual partners, tend to be faithful, and value affection and intimacy. By contrast, homosexual males are highly promiscuous. Among North Americans for example, 75% of homosexual men have over 75 partners in a lifetime, while 72% of heterosexual men have less than eight partners. (Symons, p. 299) These differences are not primarily cultural, but genetic. Men, straight or otherwise, seek many partners. Women don't. If women were as promiscuous as men, heterosexual men would have as many partners as homosexual men.

Yes, you are right, women are concerned with getting pregnant. But that that has little to do with why they are less promiscuous than men is shown by the fact that lesbians are not more promiscuous than heterosexual women.