In my view it's gay parenting that has the strongest potential to bring gay marriage and the gay family down, but it will take a few decades for meaningful data, and, perhaps more importantly, meaningful anecdotal evidence, to percolate through the culture. The kids/guinea pigs in the great gay experiment are going to have a lot to say once they reach adulthood, and a goodly portion of them will be talking about identity crisis, confusion, pain, anger and shame.
The pollyannas who claim "no difference" today are difficult to refute. They control the research money. The population they claim to speak for is still usually quite young and certainly still quite small. But in a few decades pollyanna researchers will be replaced by a large population of adult "children" of gays who will speak for themselves. It will be very interesting to hear what they have to say.