To be honest, because I am not gay, it is out of my jurisdiction to claim that I know the answer to this question, even moreso after clarifying my prior point.
I know a guy who had no sexual drive for the first 20 years of his life and he did not understand why. He thought he was gay but couldn't fathom living with that fact. Eventually he tried making out with girls and slowly did he develop the niche he was seeking.
I'm sure some people can be born with an attraction to men, however. Regardless, whether you like men or not, that does not change the fact that naturally you are defying the progression of human life if you marry gay.
Edit: To respond to your last point, "most people of intellect" is a redundant and subtle shot, something I could anticipate from the beginning of this discussion. Anyway..
The point is, we are talking from an ethical perspective, so yes while there is overpopulation at the moment, chances are there will not be forever, specifically if more and more people marry gay over the long haul.
I would also like to point out that the overpopulation argument really is not compelling enough to tell people, "stop reproducing." We love of our children, and we love to see them blossom. The greatest thing in this world is life as we understand it and we are rescinding our chances of progressing society by cutting off this very given possibility.