My Guess about the Long-Term Effect of the Gay-Marriage Controversy

There will be little effect.

“Families” that don't produce that many children won't pass their memes on to the next generation.

A century from now gay marriage might be seen as an obvious irrelevancy that was not even worth opposing. As I have said before:

As for whether we should pay attention, if medical research stagnates the anti-natalists will disappear. On the other hand, if cryonics actually pays off we might have them to kick around forever. At first, they will be outvoted in elections and outbid in decision markets. Later they will be ignored completely as they become an infinitesimal fraction of the population.

The above reasoning explains why traditional religions allowed the elderly to get married even though many of the arguments against gay marriage might apply there. Old marriage was not worth opposing.