"To die for an idea," Anatole France once wrote, "is to place a pretty high value upon conjecture." Presumably this goes double for having others die and suffer for one.
I was thinking a bit more about the "strong" case against gay marriage. By strong, I mean ones that try to take seriously the moral equality of gay and lesbian individuals, that claim to not be predicated on homophobic degradation, but instead about maintaining the stability of what they take to be an essential social institution: marriage (folks like Robert George spring to mind, though the way he presented his argument here seems somewhat different). The claim, as I understand it, is that allowing gay marriage weakens the social value and meaning of marriage as a whole. To the extent that a strong social consensus around the value of marriage is important for societal welfare, then gay marriage can justly be opposed as a potential threat to the institution as a whole. As for civil unions, the argument as I've seen it is not adverse to some mechanism for allowing gay couples to secure most (if not all) of the rights accorded to heterosexual couples, but they worry that gays and lesbians won't be "satisfied" with civil unions, and sets us down the slippery slope to gay marriage. Because the bottom of the slope is so dangerous (they argue), we cannot risk setting down the top.
As I said, I was thinking about this, and I just don't find it remotely persuasive. I barely think it even has a claim to moral seriousness, if we unpack it. So, to the extent that this is the best that can be done ... no. Not flying.
The first concern I have when I hear this argument is that the ship may have already sailed. It is not clear to me that we have a unified definition of marriage in this country any more (if we ever did), and what's more, the exclusion of same-sex couples from marriage is doing at least as much to "degrade" the perception of marriage as an institution amongst liberal-minded persons as their inclusion "degrades" marriage amongst traditionalists. Indeed, if anything it seems like the former effect swamps the latter: I do know of progressive-minded folk whom are deeply ambivalent, at best, about marriage, precisely because they see it as a heterosexist and bigoted institution, one that they may not be able to ethically buy into.
By contrast, I've never actually heard a marriage-traditionalist put their money where their mouth is and actually say they feel like their marriage is directly diminished in any way by the inclusion of gay couples, or that they are at all more ambivalent about getting married or participating in the institution of marriage as same-sex marriage spreads. Rather, they posit a considerably more indirect mechanism: They worry that other people -- the unwashed middle -- will progressively lose touch with value and sanctity of marriage, and that this in turn will make all marriages less meaningful.
This raises the second issue I have -- whether the conservative belief is actually falsifiable. If conservatives were making a personal claim -- "If gays are allowed to marry, then marriage isn't worth it for me" -- this wouldn't be an issue; it would simply be a matter of subjective personal preferences. Likewise for various deontological arguments one could make (that celebration of gay commitment is simply wrong, or, for pro-SSM advocates, that access to marriage is an essential component of human dignity). But the claim they seem to be making (about gay marriage's effect on other people's perception of marriage is an empirical one, and, for the reasons stated above, one I'm exceptionally dubious about. I'm exceedingly skeptical that gay marriage actually has any significant detrimental effect on marriage as an institution (if anything, I predict having a positive effect). So suppose 20 years from now we have a mountain of data in front of us, and it tells us that gay marriage exhibits no noticeable effect on the public's reverence and respect for marriage as an institution. Does their opposition melt away? I'm not convinced it does, because I think the tail is wagging the dog here -- the core belief is that gay marriage is bad, and any empirical scaffolding is just an apologia to try and attach the belief to something that at least gestures at respecting gay human dignity. If it falls away, they'll find something else.
But what of the risk I'm wrong? And here's where we return to Mr. France. Is there a non-zero risk that allowing same-sex marriage will have catastrophic social consequences? Sure, in the sense that there's a non-zero chance of essentially anything causing anything (there's also a non-zero risk that not allowing it will have catastrophic social consequences).
But it is conjecture, and thin conjecture at that -- dependent as it is on presumptions of what everyone else (but not me, of course!) will undoubtedly do as gays get married. It's a prediction that gets harder and harder to sustain each year. And in the meantime, that conjecture is weighed against the concrete material deprivations marriage inequality foists upon gay couples right now. We know that gay couples are sharply restricted in the rights and privileges that they can access vis-a-vis heterosexual couples. We know that even half-steps like civil unions are bitterly opposed by anti-gay marriage advocates because of the risk they'll lead to gay marriage -- putting yet further tangible barriers between gay couples and full equal rights. All of this is justified by ... conjecture, and seemingly a rather weak conjecture at that.
In this light, opposition to gay marriage ends up looking kind of like putting up a minefield in one's front yard to guard against a Canadian invasion. Is there a non-zero chance Canada is out to get us? Yes. If the Mounties do come streaming across our northern border, will the mines come in handy? Yep. But for the time being, that conjecture about Canadian intentions is having the tangible effect of blowing up a bunch of neighborhood kids, and in the face of that rather concrete harm one really can't ethically rely upon such thin conjectures.