Lately, I've been thinking about two seemingly unrelated arguments against same-sex marriage. One is that we shouldn't change the laws of marriage, which apply to the heterosexual majority, for the sake of accomodating the homosexual minority. The other is that if we are going to allow same-sex couples to marry, why not allow polygamy or incestuous marriage. My most detailed response to the latter argument came last February in a series of two posts and a follow-up. I just wanted to emphasize one point that might have gotten lost in all of that. And it relates to the first argument above.
Same-sex marriage, at least in Masachusetts and several other states, would not change the laws which govern the marital relationship. Same-sex couples would be subjected to the exact same laws that currently apply to opposite-sex couples. Likewise opposite-sex couples who marry would continue to have the exact same laws apply. For example, should same-sex marriage become legal in Connecticut, the laws which govern my marriage to my wife will not change. One can argue--and we certainly do--about the cultural impact of allowing SSM, but in terms of the law the only change would be which couples may enter into marriage, not the legal consequences of marriage. Polygamy, on the other hand, changes a law which governs marriage and it changes it for everybody. Whereas the law now says a married person may not remarry without obtaining a divorce, it would no longer require that. Although this is not the only problem with polygamy, it is a serious one. I believe it would have a significant detrimental impact on the marital relationship. Likewise no-fault divorce changed the laws which govern the marriage relationship itself. The rules for what may end the marriage changed, and this quite naturally had an impact on the marital relationship. Again since the laws changed for everybody, its potential effect reached everybody. Even those that don't get a divorce are aware that divorce could happen even if they do nothing wrong.
In some sense, changing the prohibitions with regards to incestuous marriage is more like the change in same-sex prohibitions in that, with regards to marriage, it is a change of who may enter into the relationship and not a change of the laws which govern the consequences of marriage. But such a move does indeed change the laws which govern those other kinship relations. So just as legalized polygamy and no-fault divorce could impact the marital relationship, legalized incestuous marriage could impact other family relationships. In this respect alone I see a huge difference between same-sex marriage on the one hand and no-fault divorce, polgyamy, or incestuous marriage on the other. And, of course, there are other differences as well.