You knew this was coming -- the New York Times' "Room for Debate" subject this week is polygamy. Of the mini-opinion pieces, 4 of 6 are pro-polygamy. One argues against based on women's status in polygamous cultures, and one actually raises the issue of the impact on children.
How long before the first lawsuit is filed seeking legal recognition of a polygamous union? Probably from a Muslim family, in which the wives are both legally recognized abroad in a Muslim country, where, upon moving to the U.S., one loses that legal status.
Ann Althouse wrote very strongly in favor of gay marriage on www.althouse.blogspot.com, and her consistent response to the question of polygamous marriage has been, "marriage is a legal relationship between two people, and only two, because I say so." But all the legal arguments in favor of gay marriage can be applied to polygamous marriage, and all the arguments against it have been rejected by courts and by legislatures. Fundamentally, in deciding for gay marriage, courts have seen marriage as a matter of favoring personal liberty and of opposing discrimination against sexual minorities, and have disregarded any claims that there's an overall social good (e.g., "for the children") in limiting marriage to male/female pairings. And people in secular "poly" relationships claim that it is their "sexual orientation" to only be fulfilled in a relationship in which they love, and have sexual relations with, multiple people at the same time.
What's more, the overriding priority of "favoring personal liberty and of opposing discrimination against sexual minorities" extends beyond legal marriage, and trumps religious freedom and any state interest in favoring any one family type over another. Bakers forced to bake wedding cakes with "congratulations, Adam and Steve." Fertility specialists forced to treat lesbian couples, even when they're seeing artificial insemination not due to infertility but simply as a way of acquiring sperm. Adoption agencies obliged to give same-sex couples the same chances at adoption as straight couples.
But, you say, what about all the practical ways in which a three or more person "marriage" is more complex than a two-person one -- inheritance rights, medical decision-making, Social Security benefits, etc.? The government didn't let "complexity" (that is, the rising issues of three or more parents, when the state legally recognizes two mothers or two fathers, and yet there's a biological father or mother in the picture as well) get in the way of same-sex couples. And legal recognition of multiple wives would cut down on welfare abuse that exists in polygamous families now, in which the second and other wives claim welfare benefits as "single mothers" (this is the norm in fundamentalist Mormon families here, and in polygamous Muslim families in Europe).
That's not to say I favor polygamy. But it'll be interesting to see how this plays out. And the Althousian response of "just because" isn't going to cut it in defense of the two-person marriage.