charles, I'm tracking what yer saying. The government has an interest in protecting rights as they should. Since the term "marriage" is loaded, with traditionally and historically recognized ties to religion, I would advocate that the government have no role in that.
If the government however chooses to allow 2 life forms to be recognized in a civil union for contractual purposes, taxes, property ownership, estate, etc. then that is another matter entirely. I think it makes the whole conversation cleaner if the issue is simply a secular conversation over legal rights, as opposed to redefining values and morality. Now the state should set limits on who can enter a civil union (i.e. willing, age of consent, able to consent, etc.) and that vote may be influenced by the morality of the constituency. But if you want to get "married" go to the church, and they have their own standards of who they will and wont marry.
That said, I remain convinced that the gay rights movement is not interested in legal rights; they want it all. They want all religions to conform to their view, and for the government to force them to do so. I am presently licensed to perform weddings in the state of Hawaii, which I will forfeit the moment it ceases to be a matter of conscience and I am required to marry anyone that asks. They have already made it law that landlords must give preferential consideration to rental applicants on the basis of their sexual preference, in the name of protecting homosexuals. There are those in this state that think the government should be able to force me as a clergyman to do their bidding, and that ain't gonna happen.
And that is what the 1st amendment is supposed to protect us from.