Maybe that's what they mean when they say that same-sex marriage "redefines" marriage, as if it redefines marriage as a freely chosen partnership, rather than as their unspoken definition of chattel slavery with gifts and cake.
I have always, too glibly, said that if gay marriage affects your marriage, then one of you is gay. But maybe The Bad Straights saw something I didn't think of, that The Gays are modeling what marriage could be, for anyone.