One of the things Genevieve Wood brought up at the forum was the analogy of the movement for same-sex marriage to the movement for no-fault divorce. (Her comments on this matter occur at 31:30 in the recording) While the movement to eliminate prohibitions on interracial marriage is the favorite parallel of many advocates for same-sex marriage, the no-fault divorce parallel seems to be a favorite among many of those opposed. In both cases the parallel is generally brought up as a response to particular claims. In this case it was brought up by Wood as a response to the common claim of "How does same-sex marriage affect opposite-sex marriages?" She says that the same question was asked about no-fault divorce, namely "How does the no-fault divorce of an unhappy couple affect the marriage of somebody else?" And yet no-fault divorce has had a great impact on other marriages with divorce and cohabitation rising. She says marriage is a public institution, and that's why there can and will be a broader effect. I certainly agree that marriage is a public institution, but that doesn't really answer either question as to specifically how the other marriages are affected. So let us look at the comparison a little more closely to see how each change in marriage might have some broader effect.
The first difference I see is at the more direct level. Many of the harms from no-fault divorce come immediately from the divorce itself. That is the children of the marriage, in some if not many instances, would be better off if the couple remains married instead of the parents getting a divorce. I have yet to see anyone argue that the children of same-sex couples would be better off if the couple remains cohabiting instead of getting married. (Wood refers to arguments over the welfare of these children "emotional blackmail", but that's an issue for another post). So we see that already on the immediate level there is a big difference, and we will see how this difference can play out in the broader impact.
Part of how no-fault divorce impacted other marriages was through an imitation effect. As divorce became more common, people went into marriages without as much certainty that the marriage would last. This could become a self-fulfilling prophecy in at least two ways. One, people might be more reluctant to make personal sacrifices for the sake of the marriage with the knowledge that the marriage could end and they would have to be prepared to fend for themselves. Secondly, when times got rough, divorce was seen as a more realistic alternative. And then you have those that became reluctant to marry in the first place because of the rising divorce rate. Why marry just to divorce later? Especially vulnerable to this imitation effect are children of divorce themselves. If same-sex marriage has an imitation effect it would mean more people deciding to marry instead of cohabit. The demand for marriage is certainly a testament to its worth. Again this imitation effect is especially true for children of same-sex couples who could now grow up with marriage as a model instead of cohabitation. Furthermore, withholding same-sex marriage would continue to lead to a proliferation of marriage alternatives like domestic partnership plans that are open to oppposite-sex couples as well. Just as divorce became a more realistic alternative to remaining married, these programs as well provide opposite-sex couples many realistic alternatives to marriage in the first place.
This leads us back to another direct effect of no-fault divorce. No-fault divorce changed the rules of every marriage. Even for a couple that did not divorce there was always a chance of it occurring. Every marriage has at least a chance of going through some rough times. No-fault divorce made it at least a little more difficult to remain married through those times. With same-sex marriage, though, the same rules still apply to opposite-sex marriages. They just apply to other couples as well.
Later in the forum (1:11:20) Wood was asked whether she would support an amendment for a uniform national policy on divorce. She said no, because divorce did not alter the definition of marriage. I disagree. Whether marriage is a lifetime commitment, or just a temporary arrangement seems to me to be a much bigger difference in the definition of marriage than viewing one's spouse as a human being without reference to gender.
While I think lessons can and should be learned from the no-fault divorce debate, for example changes can have unintended consequences, I do not think the mechanism fits the same-sex marriage scenario very well. Nor do I think that such lessons forestall any change. We should take any claims about potential harms quite seriously, but we also need to carefully examine how such harms may come to pass.
UPDATE: Eve Tushnet responds with an additional difference and a dispute. Her difference is that divorce is not viewed as an ideal, whereas same-sex marriage is. I agree with this difference, but I see SSM as upholding marriage itself as an ideal. For it is allowing marriage over the alternative of cohabitation. I don't see it changing whom the ideal spouse is. For most Jewish mothers the ideal will still be a doctor.
She disputes the claim that divorce is a bigger change in definition, since many societies have had rules for divorce whereas viewing one's spouse without regards to gender is a late twentieth century innovation. I agree that the latter is more novel, but marriage has been progressing in that direction since the early nineteenth century. Which is a bigger change in definition depends on what specific change we are referring to. In general I'd say the exit requirements of marriage are more fundamental to its definition than the entrance requirements. As for the specifics I do see certain changes in divorce laws as greater alterations than the change from egalitarian marriage to allowing same-sex marriage. In regards to Jewish divorce, I would note that even that was rather a novel concept from my understanding. I don't believe other cultures at that time allowed a woman to remarry after divorce. (A man could of course remarry, but then a man could remarry even without a divorce). But much of this dispute I think comes down to what changes are "definitional" and what is a variation within that definition, a topic about which I hope to write soon.