I have always wondered why the government is involved with marriage at all. Seems like it would be simpler if we set it up like this:

Everyone pays the same taxes no matter what, and you better write an explicit will and testament to control who gets your stuff when you die/can pull the plug on your vegetative state. Ie. no special benefits/drawbacks for married people.

If you want to get married, great---go find a church or a mosque or a ship's captain; it's none of the state's business. The government doesn't recognize the institution of marriage as anything special. Marriage would be an entirely private association, like joining the Elks lodge or something.