The flaw in your reasoning is that it oversimplifies modern evolutionary theory. This is a great starting point on the subject of homosexuality and evolution: http://www.adherents.com/misc/paradoxEvolution.html Trust me, it’s a long read, but it is more than worth it.
What I find curious is that you emphasize that you are a man of science, not faith, yet you reject the rational minds of today in favor of the wisdom of times gone by. Science and medicine advance. Long gone are the days of female hysteria, leeches, and shock treatments. I would find your position much more understandable if you were a creationist or something similar, but as it is, I’m puzzled.
I've read that before, and others like it. It states that homosexual conduct occors in nature, therefor it's natural and the logical conclusion that they wish you to draw is if it's "natural" then it's normal. Bollocks. Blindness, spina bifida and even mania or emotional distress occur in the mammalian population naturally. But, that hardly means that animals (including humans) that suffer from those disorders are "normal".
If you look at the reasons that the AMA, or the WHO (Incidentally, the WHO actually passed a "resolution" to reclassify homosexuality - Who bases science on a policy vote?), changed their positions on homosexuality, they're political reasons, not scientific ones. The reasoning behind re-classifying homosexual behavior from a disorder to an acceptable sexual variance was based on nothing more than political pressure.
Moreover, while there has been research to find the "cause" of homosexual predisposition or behavior, many of the findings or conclusions have been pilloried by the homosexual lobby, in much the same way as Miss Prejean was attacked.
As an example, there has been some tremendous research done about hormonal imbalances found in some pregnant women that may result in changes to neurological development of babies in utero. It is theorized that if you could test for these imbalance, it may one day be able to predict with some accuracy a child's homosexual tendencies. If you could identify a genetic or hormonal "trigger", then you could then begin to formulate or design a "fix" or prevent it from developing in the first place. This is the part the homosexual lobby objects to, as they believe that there's nothing to fix.
Look at where this scientific political correctness has brought us to today. Recently, we had news stories about a "man" who gave birth to a baby. An 8th grader knows that it's biologically impossible for a man to give birth. Because of the pressure of political correctness, psychiatrists today enable people that believe they're "born into the wrong" body - enable them to make profound physical changes to their bodies, all based on the premise that it's "natural" and normal. And surgeons indulge this disordered thinking by helping the victims to mutilate their bodies - what ever happened to the medical credo, "First do no harm"?
Just like we shouldn't base science on religion and certainly shouldn't allow religion to creep into the science classroom in any way, science shouldn't buckle to political correctness, which is exactly what it's done with respect to the homosexual phenomenon the last 40 years.