Advocates of "gay marriage" or homosexual civil unions argue that promiscuity will be reduced. Such an argument overlooks two key points. First, a embracing homosexual unions is more likely to undermine the institution of marriage and produce other negative effects than it is to make fidelity and longevity the norm for homosexual unions. Second, homosexual unions are not wrong primarily because of their disproportionately high rate of promiscuity and breakups. They are wrong because "gay marriage" is a contradiction in terms. As with consensual adult incest and polyamory, considerations of commitment and fidelity factor only after certain structural prerequisites are...