At long last, I think I have come to the point at which I am satisfied with the Libertarian position on Marriage. Ken Starr is now as we speak, arguing in defense of Proposition 8. He says:
"I've seen very thoughtful Christians say, 'Get the state out of this. ... If you want to be married by your priest, rabbi, minister, pastor, great -- call it whatever you want. [But when you're] welcome to city hall, it's a civil union.' That may be the eventual way that we need to go, because you see the culture war that is so unfortunate."
I also like his phrasing, 'may be eventual', rather than inevitable.