One of the more popular arguments against the legalization of homosexual marriage is that it will open the door to polygamous marriages, cross-species marriages, incestuous marriages, etc.  The argument is often dismissed as a “slippery slope” that is unjustified.

I have argued in the past that properly construed, the argument isn’t a “slippery slope” argument at all.  That is, society may in fact never legalize polygamous marriages.  However, the society that acknowledges homosexual marriage will have no principle to fall back on to prevent polygamous marriages.  Hadley Arkes, in his excellent essay “The Family and the Laws,” makes the same point:

We’ve also learned over the ages that the law teaches:  If the law becomes open to the arrangements of mothers and sons, fathers and sons, marrying, we can expect that these arrangements will not stay rare and bizarre–that we will come to see far more of them.  But whether we see more or less, the people who claim rights of same-sex marriage have to deal with this critical problem of their argument:  that they have no ground in principle to deny any longer any of these other arrangements.  They cannot explain why marriage should be confined to a couple, rather than the ensemble of three or four or more who claim to be intimate and loving.  Some of us made this argument eight years ago during the hearings over the Defense of Marriage Act.  And sure enough, as though sprung from the argument itself, we have now seent he advent of the “polyamorous,” the people who claim a right to be joined in marriage to the fuller range of people they are capable of loving.  But if the notion of marriage comes to encompass the polyamorous or the polygamous, or the father and son, or the two brothers, the notion of marriage will have lost its coherence.  And along with that coherence, it will have lost the most compelling ground of its explanation and defense, as something desirable, something we are justified in preserving.

If “marriage” is constituted by intimacy, regardless of the possibility of procreation, then there is no possible grounds on which any intimate relation could be barred from marriage.  As Arkes goes on to point out, an erotic attachment wouldn’t even need be necessary:  two sisters taking care of an elderly father might want to marry in order to take advantage of special provisions for insurance, joint tax returns, etc.
The question of homosexual marriage is not a question of who we should allow into the institution of matrimony.  It is a question of whether marriage should exist as a meaningful idea at all, or whether we wish to remove the principle that undergirds it, a principle that demands the monogamous union of a man and a woman.

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Posted by Matthew Lee Anderson

Matthew Lee Anderson is the Founder and Lead Writer of Mere Orthodoxy. He is the author of Earthen Vessels: Why Our Bodies Matter to our Faith and The End of Our Exploring: A Book about Questioning and the Confidence of Faith. Follow him on Twitter or on Facebook.


  1. Blaming homosexual marriage for “opening the door” to polygamy is like blaming rock’n’roll for opening the door to the Charleston.


  2. Matthew Lee Anderson May 5, 2008 at 8:52 am


    As far as I know, polygamy isn’t legal in the United States and probably won’t be before homosexual marriages. I’m confused as to how your analogy fits what I’ve written.


  3. The slippery slope argument is indeed compelling. What I like about it is that it illustrates the true purpose of favoring a limited legal definition of marriage: theonomony. Christians want America to be a Christian nation. They want the United States Government to be a Christian Government. There is no other rational explanation for this behavior.
    What is unfair about marriage in its current form is the privileges it affords to those who enter the contract. A state – sanctioned marriage certificate is a convenient discount coupon when dealing with the government.
    To be just we ought to do one of two things: extend the privilege to others who enter into voluntary contracts, or disable the franchise. People are loathe to relinquish a privilege, even Christians, though we are commanded by Christ to forsake all privileges.
    I doubt that either will happen.
    Nathanael Snow


  4. Matthew Lee Anderson May 5, 2008 at 10:13 pm


    I am not at all clear why arguing for excluding homosexuals from the institution of marriage entails that one is a “theonomist” or a proponent of a “Christian nation.” I am, in fact, neither of those. One need only turn to that pre-Christian Plato to see that there are reasons outside of the Bible to be concerned about the State’s view on marriage.

    I don’t see how the State providing certain privileges afforded to some citizens and not other is “unfair.” One could argue fairly easily that the State has a vested interest in marriage, which would entail that it ought provide certain incentives to pursue it (which it currently does).

    I think I disagree with your notion of “justice” as much as I disagree with your view of marriage. To view it as a voluntary contract ignores the natural basis for marriage upon which the laws are (or ought be) based.


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