Interesting that some people who think about these things are now arguing that in opposing same-sex marriage, social conservatives may actually be encouraging the legal recognition of such relationships, and in fact hastening the demise of marriage as an institution!

Jonathan Rauch argues in the Atlantic that the last thing supporters of marriage should be doing is setting up an assortment of alternatives, but that is exactly what they are doing, and not only for gays, when they offer "ABM" (Anything But Marriage).

Every year more companies and governments (at the state and local level) grant marriagelike benefits to cohabiting partners: "concessions fought for and won mostly by gay groups," as the Los Angeles Times notes, "but enjoyed as well by the much larger population of heterosexual unmarried couples."
....
ABM, perversely, turns one of the country's more culturally visible minorities into an advertisement for just how cool and successful life outside of wedlock can be.