"It was somewhere around 1982 when I first heard the “born gay” concept, and it took me twenty years to figure out that people can actually deceive themselves into believing that they were born “gay,” whilst common-sense observations about the human species prove them wrong."
On the contrary, common sense observations of the human species fully supports this notion.
"The “born gay” concept is in direct opposition to the ridiculously obvious pattern of human reproduction. Human beings reproduce sexually."
Oh, so that's how we do it! Well, I'll be damned.
"This means that people who say that they were “born gay” are, in effect, saying that nature has chosen to remove their ability to reproduce."
That would just be silly. They can still, and at times do, reproduce. They're simply not attracted to the opposite sex. That doesn't mean that they're sterile or something.
"Nature doesn’t do that."
Correct. Nature does, however, make a certain percentage of a given population in quite a number of species--humans included--attracted to their own sex. My own personal hypothesis on this is that it's a form of population control without loss of productivity to the group or community as you would have with a lower birth rate, for instance.
"Nature is, very obviously, dedicated to the reproduction of all species of life. Why would nature create a life form with millions of cells and remove that life form’s attraction to the opposite sex which is necessary for the propagation of the species?"
See above for my thoughts, though I doubt highly that you would find that reasonable or rational given that you didn't come up with such an obvious benefit on your own examination of the problem. In other words, your argument boils down to "It's icky!" and that's where you'll stay, despite all evidence or explanations to the contrary.