Nah, I ignored that treatise because of the length.
But, if it's a principle, it's a principle, no matter how common they are.
Compared to straight people, gay people aren't that common either.
Law is always under/over inclusive. It's always a rough approximation. I can drive safely at 40 mph in the city, but speed limits don't take that into consideration. They address us all as a populous, even though that's under/over inclusive. I don't get a special dispensation. Think about how unworkable it would be otherwise. We'd have to all undergo a "driving abilities" test to determine, not just that we can drive safely generally, but at what speeds, under what conditions, etc. And that's just for speed limits. Now apply that to marriage--if child bearing were to be a requirement, we'd have to evaluate fertility, child bearing intent, etc. In addition to its unworkability, think about the governmental infringements on personal information that would entail.
Male/female is a rough--but good--approximation for child bearing. The state has an obvious interest in creating and fostering the young. Thus, male/female relations should be given special status. This really isn't that difficult to comprehend. Whether you think it is "unfair" to homosexuals is a different matter entirely. We've been ordering our societies around this principle for centuries.
And as for the "unfairness," I think that homosexual unions should also be given special status because, I think, the state also has an interest in generally fostering loving relationships even if, in the mine run of cases, those relationships can't produce offspring. This interest, however, isn't as important as child bearing/rearing, so it shouldn't be called "marriage." It's something lesser--good, nonetheless, but lesser.
Reasonable minds can disagree, but the reaction on this board to this point of view is mind-boggling to me.