I think we're only talking about the law here--at least I am. And as far as I know, the American *legal* institution is called "marriage." (Somebody correct me if I'm wrong) Civil unions only came into being when gay couples wanted the legal benefits associated with marriage. And what did they get? Something inferior, when they got anything at all.
Let the churches rail against it and deny gay couples marriage. So what? I'm pretty sure I can't go into a Catholic church and get extreme unction just because I'm curious about it, either. The church refusal shouldn't prohibit them from going to city hall and getting that piece of paper.
Curtiss