Balderdash.
You don’t know what you are talking about. I live in a jurisdiction that has gay marriage, and we are having endless fights, not over gay marriage, but over polygamy now.
It’s not an ancillary issue, it’s central to it. You lose here, you aren’t getting that other stuff back because you’ll be too busy fighting the next thing down the line.
You’re having endless fight not because marriage is losing. You’re having endless fights because marriage has already lost.
Polygamy and gay marriage are natural extensions of the idea that marriage and family is about self-fulfillment and individual happiness rather than about duties and obligations and responsibilities.
Marriage isn’t saved by preventing same sex marriage, that the easy thing to do, the harder part to get straight people to marry, and then honor their vows.