Anyone with half a brain recognizes that same sex marriage poses no threat to the sanctity of traditional marriage whatsoever, and that those assertions by religious groups are at best poorly disguised lies. I have to wonder though if Gay Marriage won't weaken religion, at least indirectly.
This story is recent, but not unique; an Illinois Foster Care Group has lost a contract with the state because they only place children with married couples, excluding same-sex couples (as Illinois has only legalized civil unions). What this means is that they will lose a huge chunk of state funding along with the ability to place children that have been taken into custody by the state. (They will still be able to place children that are not in state custody.) This kind of thing has been happening to a lot of agencies that have ties to both religion and adoptive services. The end result is unaffiliated agencies placing children in a more diverse set of homes (which sounds great for the kids, but you can believe religious groups don't care about them).
If fewer children are placed in the custody of cherry-picked religious homes, it stands to reason that fewer children will be indoctrinated (hey the right doesn't have a monopoly on that word) by said religious parents. That sort of thing should only accelerate the acceptance of more secular practices (LGBT rights being one of them) while further marginalizing religion. (Especially since LGBT couples, even if they retain ties to their faith, might not be so willing to bring their children up in a religion that has denigrated them for years.)
At least that's my pondering of the night, and that's all it is right now. With only a few states legalizing same sex marriage so far and some models predicting that the legalization in all fifty states is as much as ten years away, we've still got a long way to go. But it makes me wonder...