I have 8 kids and a good stable marriage. We have several gay couples living together within 3 blocks of our house. Whether they are shacked up or pseudo-married makes little difference to my kids as you suggest. But as the writer suggested sexuality is a rather mystical thing and the more of it you are exposed to the more it effects your. As gay couples gain boldness to flaunt their sexuality the effect will increase. I have spent quite a bit of time explaining sexuality to my kids and they and I are repulsed by sodomites. But there are many many disfunctional families out there and they are much more susceptible.
It is all just another drop in a bucket. How much did 3's Company do to promote gayness, how about Monty Python? All of these things are straws on a camels back. Gay marriage is a big one.