Which part of the math do you not understand?
The part where 2% to 4% of the population who are gay suddenly and inexplicably turn into a 100%, for a start makes little sense.
If two gay men are to have children, this obligates at least one woman, somewhere, to relinquish her child.
No it doesn't, shared parenting is quite common, and it is the way children are raised in a caring and loving environment that determines how well adjusted they will be as adults, not how many parents or grandparents they have. Children are not born with knowledge of such bigotries and prejudices, it takes adults to shameful teach them this.
How long can this be sustained.
Anyhow, just drop it, you're speaking in hypotheticals which are entirely implausible, unnatural and extremely unconventional.
That's pretty ironic given it was you who created this hypothetical where everyone was gay, you still haven't said why, even after I have asked several times.
Just accept the fact that there are no species of animals that donate their children to others, outside of an extremely small demography of humans.
Firstly only you are suggesting this, and secondly many species that live in societal groups share parenting of young, again your ignorance of the natural world is pretty surprising. Just as homosexuality is prevalent among many other species as well, and thus us perfectly natural, despite you claiming it was not.
The only desperation I see, are the futile attempts to decry people who happen to be gay, even when they harm no one, and live a loving relationship between consenting adults, and live happy, productive and fulfilled lives. Ultimately such bigotry comes down to archaic biblical passages, archaic morals that are demonstrably pernicious, and should have no place in modern morality, for that reason.