In fact I read some time ago that one mutation that does have a small contribution to sexual orientation, has the same allele frequency in most Human population

In fact I read some time ago that one mutation that does have a small contribution to sexual orientation, has the same allele frequency in most Human populations, suggesting that even the "gay" allele is positively selected for. A Human individual's fitness affects the chances of his whole family. And it's just not true that Homosexuals don't have children. In practice they have fewer children, but more than you might think.