Right, but now you're talking about rights, which are important, but are they the institution of marriage? I tend to think that the whole is greater than its parts. We can make the case that civil unions are not equal because they do not convey all the rights of marriage, which should be conveyed, but does this leave the door open for promoting civil unions that are equal to marriage in respect to all rights conveyed? Would this make civil unions equal to marriages? I would think no, that the two would have different meanings attatched to them. Of course, if this type of CU was allowed for SS couples, it would have to be allowed for hetero couples as well. But that would present a problem...why would someone choose to get a CU if they could be married? And, supposing that many people did, how would that effect the meaning of marriage? Hmm, it seems that granting SS couples CU that confer all the rights of marriage may be worse for the "institution of marriage" than just allowing them to marry...
You know, I used to think there was a difference between CU & SSM, but now I have no idea what that difference is. I think that marriage is in a funny position because it's both a religious institution and a civic/secular one, and the tensions on it are pulling in different directions because those two sorts of things answer to different sorts of reasons. I wonder if CU would make marriage better the way that the separation of church and state makes the church better.
My fear is that if we seperate Holy Matrimony from CU's, then that move will strengthen the Church qua cultural institution. It seems obvious that the Church uses the status it already has as a cultural institution to push its poltiical agendas, and I'd rather not strengthen that. (NB, i know it's not accurate to talk about "the church" as if it were a cohesive unit, but I don't think the point is lost even so) Also, while I'm not a proselytizing atheist, I'm not enthusiastic about supporting a move that would probably drive more people to the church, which it would do, not, obviously, because of the appeal of its religious message, but because people would want to be "married."
I would argue that separating marriage from civil unions would strenghten the State more than the Church. It would free the State from the messy responsibilites it shouldn't have in the first place: that of social engineering or spiritual affirmation. The government has no business in approving (or disapproving) our relationships.
I think we are already very close to this ideal. If the State issued only CU documents to everyone, then people can continue on as they wished. Some people will want to get married in the eyes of their God, some will get married with a secular celebration, some will have a glass of champagne and call it a night. Just like it is right now.