"Basically, when a child turns out homosexual, the parents probably wonder why they bothered."
Um, that's a negative. If you love someone, and find out they're gay, that shouldn't change anything. It didn't change anything in my house. I certainly never wondered 'why I bothered.' Bothered what, having him? Raising him? Teaching him to read?
"They grit their teeth,"
No, no gritting in our house.
"and get on with it, paying lip-service to the hope that the child is happy,"
No, I actually hope he is happy. I can't imagine what sort of monster would stop loving their kid because of their sexuality, much less stop wanting their happiness.
"but I doubt they particularly enjoy the experience."
I think a pretty generic 'fuck off' satisfies any required response to this piece of bullshit.
"If it's an only child then it's a probably a disaster for obvious reasons."
What reasons...? OH! You're thinking of grandkids! The idea that _I_ can only love my kids if they're going to give _ME_ grandkids to spoil.
Well, fuck off, again. I have three sons, and the gay one is not my least-likely prospect for offspring. So even if that were a priority, rather than just something that came up one time over Scrabble, you're wrong.
But, hey, you've been fractally wrong the whole time, anyway. Wrong at every scale, from ever angle, from every starting point...