FYI, I gave a shot at a secular, anti-gay argument (just for the sake of argument) in the comments here.
That's just the sort of argument I think won't work, because it rests on a metaphor ('boundaries') that has to be cashed out. I suspect that if it's explicated in a way that has some force, it'll rely, at least implicitly, on God, or, even worse, on Aristotelian teleology. Without those, conversely, it won't carry any moral weight.
The problem with my attempts is that I'm pretty wedded to the idea that claims about wrongs have to be backed up by some harm or negative effect; the symbolic stuff doesn't cut it by itself. And this is presupposition makes it hard to get to an anti-SSM conclusion.
It definitely doesn't work as an argument, though I think it could work as political rhetoric.
By the way, rereading your post, I'm not sure this part is true: "the extension of rights to same-sex couples does damage to the very concept, in a way that extension of rights to black citizens did no violence to the concept of person or citizen." Making blacks "persons" was in fact a change, no? (Not a change made by Loving, but one that had to occur for the decision to be possible.)
I don't mean to endorse the quoted claim, just to suggest it as part of the hypothetical argument. The thought is that in the race case, there's a change at the periphery, or no change at all in the conditions for the correct tokening of the concept, but in the marriage case, it's a more radical revision. Or, it's 'closer to true' to say that "'marriage is between one man and one woman' is analytic, or true in virtue of the concepts involved" than it is to say "'voters are white' is analytic, or true in virtue of the concepts..." Voters were only contingently all-white, as it were; the concepts were the same all along, and our conceptions changed.
Now I don't think we ever settle substantive issues by appeal to conceptual truths, so this line won't convince me, but it seems to be what's behind the talk of definition, of what marriage is, and so on.
You really have to disaggregate the question of same sex marriage from civil union.
SSM means the Church changes the text of the Sacrament of Holy Matrimony from gender specific to gender neutral.
CU means that the State extends the current definition of 'common law' to same sex couples. This gives 'shacking up' standing.
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If you abandon the term 'marriage' then you create a separate but equal standard that would be tolerated by the religious. You can consign gay couples into the same murky netherworld given bright lines by family courts who deal with people who shack up.
Let us not forget how Disney and many other corporations have extended many insurance benefits to gay couples during the AIDS crisis. What is wrong with the kind of activism which generated those successes? Where is the case law, oh legal scholars, that generated that new class of benefits? Or was that all corporate largesse?
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Let me repeat myself here, because I am one of those who see almost no parallels with the Civil Rights Movement in this activism. If there can be said to be a set of rights and privileges with JimCrow-like 'Marrieds Only' sign above them, why are gays not asking for those benefits based upon their citizenship. Instead of demanding those benefits as gays, they are asking to be honorary straights. This is what Marriage means, in fact it is the highest honor conferred upon straights for their sexual behavior and comportment.
What if the term 'Married' were exchanged for 'Breeder', would gay couples clamor to be called that?
Cobb,
Rosa Parks didn't refuse to go to the back of the bus because she was asking to be an honorary white. Was Rosa Parks different from the people who were allowed to sit in the front of the bus? Indeed she was, they were white and she was not. But the point is that the difference wasn't relevant to the question at hand.
Women didn't struggle to be allowed to practice law or medicine because they were asking to be honorary men. Were women different from the people traditionally allowed to be lawyers and doctors? Of course: they were women, not men. But again the point is that the difference wasn't a relevant difference.
And likewise gay couples aren't asking to be honorary straights. A couple consisting of two men or two women openly and publicly declaring their profound love for and commitment to each other is different from a couple consisting of a man and a woman doing the same, but is the difference relevant? Are gay couples incapable of the same level of love and commitment? Is shacking up the highest honor that can be conferred upon them for their sexual behavior and comportment?
The issue is not just gay couples getting the same benefits as straight couples, just as the issue for Rosa Parks was not about how comfortable the seats were in the front versus the back of the bus, just as the issue for women trying to become lawyers or doctors wasn't whether they could earn an equivalent salary in some other profession that was then allowed to women. The primary issue in all these cases is whether blacks or women or gays get recognized and treated as fully human, not as something tolerated but consigned to the back of the bus or the ghetto where the "real people" won't have to get too close and feel uncomfortable.
Legalizing same-sex marriage will do nothing to make any particular church or mosque or synagogue or temple or other religious group change its sacraments or marry couples it doesn't want to marry. Anyway there are already religious groups, including Christian churches, that perform marriages between same-sex couples.
And legalizing same-sex marriage won't directly change people's attitudes towards homosexuals and make them suddenly happily accepted by everyone. After all, blacks and women still face discrimination despite the great strides made in securing equal legal status and protection. But legalizing same-sex marriage will at least remove a badge of official sanction from such discrimination.
And yes, if back before the Civil Rights Movement those signs on water fountains, lunch counters, etc. had been changed to read "Peckerwoods Only" or "African-American Section", I would have still clamored to have them taken down.