I'm all for further strengthening the proper separation of church and state, but that's another much more difficult fight with little support. I'd like to have the option of marrying someone in the legal sense (with all the rights and responsibilities) in my own state within my lifetime.
I have the same issue against FSF redefining the meaning of "free" in software world and pretending that they have right to force their meaning of the word to everyone else. They don't.
And, btw, about that "registered union" that should replace "marriage" in legal documents ... just don't limit the number of people in there. Better yet, don't limit it only to people. Why wouldn't someone be allowed to "marry" or "register" a goat, if he likes so? And please, also drop age limits. Why wouldn't 13 year old girl have a right to "marry" another 45 years old woman, 52 years old man and their 4 years old horse? We should all have the same right, without any restrictions? Right?