He starts by stating the historical reasons why marriage exists in society:
Traditional marriage and polygamy are both solutions to the problem of paternity of children, which is a concern independent of religious sensibilities.
Steve continues with an argument against polygamous relationships, and I agree with him that there are compelling reasons for the courts to uphold the current anti-polygamy laws:
Polygamy is fundamentally dangerous to a society. On an individual level, men and women suffer because polygamy is not consistent with the biological realities of human communities. Compare this with traditional marriage, which is consistent. On the larger scale, polygamy, if it is practiced, can only be practiced by a small subset of the population, and the state has an interest to ensure that the practice is never widely adopted. But then that creates two classes of citizens, with the stresses that inevitably result from that.However, I disagree with Steve's point that legalizing gay marriage in Canada has set a legal precedent that makes it difficult to prosecute polygamy:
The only logical solution is to outlaw polygamy altogether, and apply the law universally.
But irrationality abounds, and I expect that people who are viscerally opposed to anyone suggesting that their own lifestyle choices are problematic and selfish will rally around the polygamists, as these same people did with gay marriage.
With gay marriage, the problem was that by redefining marriage to be utterly divorced from the issue of children and paternity, marriage loses its raison d'etre. Marriage becomes merely a contract of convenience for insurance purposes, or a quaint label for people who think traditions are collectibles, like those nasty little ceramic cats, and so portray themselves as "married" without a care to what marriage means or what it's for.
With polygamy, the problem is that the ability of the widespread practice of traditional marriage to stabilize society disappears, and instead we have a model of marriage that is destabilizing, and is more destabilizing the more people engage in it.
I've posted on this issue at length here and here. In a nutshell, I don't think that a society that allows gay marriage is by definition prevented from outlawing plural marriage. I respectfully disagree with Steve's argument that the institution of marriage is solely to provide stable paternity for children. There are three main purposes of marriage: the raising of children, the stabilizing and settling of the young (especially young men) in responsible relationships, and the provision of reliable caregivers in old age. For obvious reasons, gay marriage doesn't meet the first criteria but certainly meets the others - for this reason I find it hard to accept that civil gay marriage should be prohibited based on this principle alone. (Religious marriage, of course, is a different story).
Furthermore, we should try to use the long arm of the state to prohibit activities between consenting adults only when that activity causes harm to someone. I find it hard to see how gay marriage harms anyone - gay or straight - so I don't see a compelling reason to outlaw civil gay marriage. Polygamy is different - there is ample evidence that polygamous marriages cause harm to the women involved, and to the surplus young men who are ostracized by polygamous communities to maintain the supply of women for plural marriages. For this reason the state is fully justified in prohibiting plural marriages while allowing gay monogamous ones. To me, gay marriage is not about redefining a civil institution so much as extending the reach of that institution.
Religious marriage is something different altogether - most religions have scriptural & doctrinal reasons for prohibiting gay marriage and that's fine; one usually isn't forced to be a member of a church, after all. But, marriage is legally a civil institution, not a religious one. All the more reason I guess for the state to get out of the marriage business altogether & create some sort of domestic partnership & leave churches to their own devices.