Here’s another point.
I’m against “gay marriage” and gay anything for that matter.
I’ll presume that you are as well.
So here are two situations:
1. The government controls marriage. The government institutes gay marriage, which is currently happening at a hellish pace. Because marriage is a government enforced thing, businesses are forced to give benefits to “gay marriage” couples. Schools are forced to teach “gay marriages are good” curriculum. Et cetera.
2. The government gets out of controlling / licensing marriage and an adult man and an adult woman can write / sign their own marriage contract, with the terms binding only upon them. None of the horrible consequences of situation 1 happen, and divorce becomes rare. Civilization flourishes.
Wouldn’t that be dreamy, divorce, and children, and complicated 40 year relationships and elaborate estates would be so much easier without laws, and courts, and judges, and legislation, and marriage defined between a man and woman.
If you don’t want homosexual marriage, then push for a constitutional amendment, or you can legalize it nationally, along with polygamy and everything else as you are proposing.
You aren’t trying to preserve marriage, you are trying to erase marriage entirely.