Just a thought on this. It is my view that the state shouldn't be involved in marriage at all. The state should only sanction what would amount to an economic and domestic union between two consenting adults, which would have both tax and other economic consequences.
He has told you, O man, what is good ; And what does the LORD require of you But to do justice, to love kindness, And to walk humbly with your God.
Micah 6:8