Will gay marriage lead to polygamy? "If we take the step of allowing gay marriages," we are told, "we will slide down a slippery slope to polygamy." For the most part, gay-marriage advocates have been flustered trying to respond to this argument. Often, we respond with something dismissive like, "Don't be ridiculous!" Slippery-slope arguments must be scrutinized with care because the public often believes them and because they divert attention from the core issue: whether gay marriage itself would be a good or bad thing. While the polygamy argument has some superficial appeal, it ultimately doesn't work.
Slippery-slope arguments take the following form: "Proposal X contains within it a principle. That principle not only supports Proposal X but would also support Proposal Y. An honest person supporting Proposal X must therefore also support Proposal Y. While Proposal X may or may not be bad in itself, Proposal Y would surely be very bad. So to avoid adopting Proposal Y, we must not adopt Proposal X."
Substitute "gay marriage" for Proposal X and "polygamous marriage" for Proposal Y and you have a slippery-slope argument against gay marriage.
There are three possible stock responses to every slippery-slope argument. First, one might argue that the supposedly horrible destination(s) down at the bottom of the slope are not so bad, so we need not fear the slide. Second, one could argue that the slope may slide both ways, so that if we do not take the step proposed we may be in danger of sliding down the other side of the policy hill, which would be bad. Third, one could argue that we will not slide down the slippery slope if we take the step proposed because there is a principled stopping point preventing us from reaching the bottom.
In the gay marriage debate, the first stock response would involve arguing that polygamy is unobjectionable. That's an unattractive reply for reasons I'll explain below in connection with response three. The second stock response would involve claiming that if we repress gay marriage, there is nothing to stop us from prohibiting other marriages, like those involving people of different races or infertile people. This second response is the kind of argument lawyers love to make, but is not likely to impress many people as a reason to support same-sex marriage.
It's the third response - that there is a principled stopping point preventing the slide toward polygamy - that best refutes the slippery-slope argument. The argument for gay marriage is indeed an argument for a liberalization of marriage rules. But it is not a call to open marriage to anyone and everyone, any more than the fight against anti-miscegenation laws was a call to open marriage to anyone and everyone.
So, formulating the principled stopping-point, we should ask why the recognition of a new form of monogamous marriage would lead to the revival of polygamous marriage, which has been rejected in most societies that once practiced it? What is "the principle" supporting gay marriage that will lead us to accept multi-partner marriage?
One possible principle uniting the two is that gay marriage, like polygamous marriage, extends marriage beyond partners who may procreate as partners. But that doesn't work because procreation is already not a requirement of marriage. Sterile opposite-sex couples have already taken that step down the slope for us.
A second possible principle uniting gay marriage and polygamous marriage is that both exalt adult love and needs as the basis for marriage. Yet this step down the slope has also already been taken by straight couples. Marriage for the past century or so in the West has become companionate, based on love and commitment. Among straight (and gay) couples, children are a common but not necessary element of the arrangement. So even if gay marriage were justified solely by the love same-sex partners have for one another, recognizing such relationships would be more analogous to taking a step to one side on a slope already partially descended, not an additional step down the slope.
Still, how do we avoid polygamy? Here is where many advocates of gay marriage run into trouble. If we claim that gay couples must be allowed to marry simply because they love each other, there is indeed no principled reason to reject multi-partner marriages. Multiple partners in a relationship are capable of loving each other.
But satisfying individual needs is not "the principle" supporting gay marriage. Instead, gay-marriage advocates should argue that any proposal for the expansion of marriage must be good both (1) for the individuals involved and (2) for the society in which they live. Gay marriage meets both of these criteria. The case for polygamous marriage is distinguishable (and weaker) on both counts, especially the second.
On the first issue - the effect of recognition on the individuals involved - the deprivation to gays of the gay marriage ban is greater than the deprivation to polygamists of the polygamy ban. A polygamist may still marry someone if we ban polygamy; he simply may not marry many someones. The deprivation to the polygamist is large, especially if polygamy involves the exercise of his religious faith, but not total. The gay person, however, has no realistic choice of a mate available under a gay-marriage ban. The deprivation is total.
Further, there is no "polygamous orientation" causing a person to need the close companionship of multiple partners (though some people may prefer it). There is, however, a homosexual orientation, causing a person to need the close companionship of a same-sex partner. The ban on polygamous marriage is the denial of a preference, perhaps a strong one; the ban on gay marriage is the denial of personhood itself.
On the second issue - the effect of recognition on society - the differences between gay marriage and polygamous marriage are more pronounced. There is ample evidence that people who live in stable, committed couples are healthier, happier, and wealthier than those who are single. Gay marriage is a good idea because it will benefit not only the gay couple but their families, friends, neighbors, and taxpayers whose burdens to care for the gay partners singly would be greater.
While multi-partner marriages might benefit the partners involved, the much greater potential for jealousy and rivalry among the partners make for a volatile arrangement, reducing the expected benefits to them and to everyone else. In a multi-partner marriage, it may be unclear who has primary caretaking responsibility if a partner becomes sick or injured; there is no such uncertainty in a two-person marriage. While we have some evidence that children do well when raised by same-sex couples, we have no evidence they do well when raised in communal living arrangements. Since multi-partner marriages will almost always take the form of one man having many wives, they present special risks of exploitation and subordination of women, which is inconsistent with our society's commitment to sex equality.
Perhaps none of these considerations is a decisive argument against polygamous marriages. But at the very least they suggest that gay marriage and polygamous marriage present very different issues. Each should be evaluated on its own merits, not treated as if one is a necessary extension of the other.