Again, kingbee, it isn't a private contract, it is a licensed state of being; a burocratic definition. Sure, you make an agreement with the other person, but the big end of it is the contract you make with the government. You can't enter into it without the government's permission, and you need their leave to dissolve it.
While in that state you are granted the protection it affords, you are taxed differently, drafted differently, you get mandatory family leave from work, without a will the inheritance is scheduled in a particular way, when you die, your benefits pass on to your spouse, the list goes on and on.
I'd like to see how it would go with no government recognition of marriage for a couple of months. I'd LOVE to see how divorces and dividing property worked, especially among the wealthy. Without marriage defined, gay people aren't going to be any better off than they are now. The family of the dead "spouse" will still claim the "friend" doesn't have any inheritance rights, and without legal standing as a "spouse" he or she won't.
SO, we'll be defining marriage, one way or another, as much as I dislike the idea. The chaos without it would be too much and people would be even more victimized than they are now. It's honestly short sighted to say that homosexual marraige isn't any of the government's business. In reality they are the ones that are going to have to deal with the influx of "new" marriages and the conflics and demands made.