Population control: When does it become necessary?

[John Galt]

ever read the forever war? they genetically modified most of the population to be homosexual in an effort to combat population size and the main character who has had time dilation from traveling off to war and back home again is the oldest surviving solider (who is also a heterosexual) and referred to as the "old queer" by the people he ends the war with, all of whom were born centuries after him

WE COULD DO THAT