A polygamous marriage is legal, as long as it is not solemnized with a civil ceremony. In the eyes of the law, they are just “shacked up.”
So why would my arguments imply that the LDS criticism of legalizing gay marriage is stupid? I said it is stupid for Catholics to criticize people for having their own, personal religious view of marriage, while ignoring what the state sees as a legitimate marriage. Why is it stupid? Because Catholics do essentially the same thing. Similarly, I think it would be stupid of me to criticize gays for having their own, personal religious marriage ceremonies, while ignoring what the state sees as a legitimate marriage. I think it is perfectly legitimate, on the other hand, to criticize their efforts to change what the state sees as a legitimate marriage contract. That’s something the community has to decide, one way or another, and I see no reason why religious groups shouldn’t give their 2 cents on the issue.