You know, I find the most effective way of dealing with an incorrect argument is to simply point out that it is incorrect (although I have found it lately to be like shouting down a well and the frustration has definitely leaked through, I'm afraid.)

Instead of throwing SDAI into the alligator pond for being an insensitive racist homophobic bastard, we can simply note a few things:

If homosexuality does, in fact, lead to extinction, it seems odd that this trait has survived for thousands upon thousands of years. Assuming the trait is genetic, something which has not yet been proved, it is difficult to think of a trait, short of sterility, that would seem to be less likely to be transmitted down through history, yet here it is. Given the vast crosslinking and connection between genetic traits, this says to me that something quite important could be connected to the genetic trait for homosexuality. Think about it.

It should be pointed out that humanity largely left physical evolution behind, and is proceeding rapidly (maybe too rapidly) along the tracks of cultural and technological evolution.* Darwin argued that an organism's success is based on the offspring it leaves behind. From a genetic standpoint, fine. But we're past that now. Having children is a marvelous thing, and the best part of my life, but it is no longer essential to the species in the specific sense that a person who has no children is considered an evolutionary "failure." In a culture of intelligence and the ability to transmit useful information, a human being can make many other contributions to his or her species.

How many children did Jonas Salk have? Think about it.

Many marvelous things people do are completely separate from humanity's physical evolution. There is no "gene" for riding horses, ice skating, writing symphonies, reading books, building skyscrapers, growing wheat, or almost anything you can think of. We are simply fortunate to have developed a brain with sufficient flexibility to encompass these things, and they are more important than whether one has a gene for bad eyesight or, for that matter, being gay.

In other words, SDAI is simply wrong that homosexuality is a threat to the race from an evolutionary standpoint. One would suspect that the trait's very existence would be sufficient proof of this.

One can make arguments from a cultural standpoint, but that's a whole different issue.

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*I have odd theories of my own explaining why there is so much trouble in the world. Evolution pays little or no attention to compatibility of traits if neither of them is a showstopper. Intelligence and reason operate best on an individual basis, but brains capable of this are now found in animals with a strong streak of authoritarian primate--a strong instinctive tendency to want to occupy the niche of either boss ape or flunky ape. Witness the behavior of chimps, baboons, and others. In such primate societies, the loner, or individual, is a freak or an outcast.

One wonders what would have happened if intelligence had developed in a primate that was more comfortable as an individual, kind of like oranguatans.

And at least I have some real-world evidence of my theory. ;)