In spite of how clearly right I took that position to be at the time, and until just now, I have become convinced that I was wrong. I wanted to publicly acknowledge my change in opinion, in order to offer what I take to be a compelling argument in favor of the legalization of gay marriage.
That argument was offered by Dr. Roger Koppl in a discussion in the comments section of one of his posts on the ThinkMarkets blog. He point out that:
...they [religious conservatives] never objected to secular unions or calling such secular unions marriages. They are not defending marriage. They are expressing their (supposed!) moral objections to homosexuality. Why should we cow to that? Again, to protect their delicate sensibilities? No way! Certainly not given their failure to object to secular unions or the legal recognition of secular unions [as marriages].
I think that Dr. Koppl is right about this. I reproduce from my response to the post:
You do make a good point...in noting that the characterization of secular unions as “marriages” was never a matter of public outcry. I think you might be right, then, in suggesting that if there was going to be an objection to the liberalization of marriage, and its decoupling from the religious institution of the same name, then that objection should have been raised long ago. In other words, that a sort of statute of limitations applies here, and given the longstanding tradition of secular unions in this country, it might be fair to say that the window for objections has passed.
What was wrong with my previous position, then, is that I had granted to the conservatives the sacred status of marriage as currently defined, when in fact that status cannot be sustained in light of the well-established acceptance of secular unions as marriages in our country. If secular unions are unobjectionably "marriages," then it seems to follow that there is nothing necessarily sacred about marriage. And if secular unions fall within the established meaning of "marriage," I think it's pretty reasonable to think that the extension of the meaning to include gay marriages would be evolutionary, rather than revolutionary. After all, a secular union really is just a certain kind of contract, and forbidding homosexual couples from obtaining such a contractual relationship seems clearly unfair.
So hopefully that makes sense; thanks to Dr. Koppl for taking the time to discuss it with me!