To try to solve an overpopulation problem, governments (in fiction and real life) may limit the total number of children a person or couple can have; enforced with sterility, abortions, infanticide, criminal punishment, or social stigmas. Less frequently, a dystopia may try to reduce (or eliminate, if other methods like cloning or bottle babies are in use) pregnancy by banning sex altogether. However, the absolute rarest version of this trope is where the Powers That Be encourage (or require) homosexuality in some or all of the populace in order to keep the population down.
This is different from a Cast Full of Gay, which is just a story where the majority of characters happen to be gay, or tropes such as Everyone Is Gay and Het Is Ew which are about fanfiction (where straight characters in original works are turned gay for the purpose of the story). Also differs from Situational Sexuality or from homosexuality being the result of a One-Gender Race. Of course, in some universes, Homosexual Reproduction is still a possibility...
- In 7 Seeds, the teams awaken in a post-apocalyptic world and one of their tasks are to repopulate humanity. Team Autumn's leaders, Ran and Akio, absolutely hate what the government has forced them into and have banned any sex that may lead to pregnancy. This doesn't stop Ryusei and Kurumi, though, and the two of them get thrown out of the team when they learn that Kurumi is pregnant.
- In Fallout: Equestria, the Pegasus Enclave encourage homosexual relationships in order to keep population numbers down.
- Sullamander, the tyrannical Commander of the Pegasi before Hurricane in A Brief History of Equestria, wanted to implement a law like this to further cement her power over the Junta. Unfortunately, General Wind Whistler (whom Sullamander had promoted after killing the previous title holder for not being a good enough yes-mare) read up on Junta laws and pointed out that doing so would be blatant treason (not to mention doom the Junta to a slow death due to lack of replacement soldiers), and got Sullamander to back down.
- In Joe Haldeman's The Forever War, the Earth's government officially encouraged homosexuality ("homolife") to promote Population Control, which had caused worldwide food wars; eventually, they eliminated heterosexual reproduction altogether and employed cloning to perpetuate (and change) the species. With the time dilation the protagonist experiences he eventually ends up as one of the few heterosexuals and is regarded as aberrant.
- In L. Ron Hubbard's Mission Earth dekalogy, the Rockecenter Corporation (which secretly controls the world) promotes homosexuality as "psychiatric birth control."
- In Anthony Burgess' The Wanting Seed, heterosexuals are discriminated against while homosexuality ("It's sapiens to be homo!"), self-sterilization, and eventually even cannibalism are responses to overpopulation and limited resources.
- In I Will Fear No Evil by Robert A. Heinlein, the government doesn't quite go so far as to forbid heterosexual sex, but they strongly encourage homosexuality for this reason.
- In Charles Beaumont's "The Crooked Man," homosexuality became the norm but heterosexuality was tolerated for a while. Then a politician demonizes straights and they are forced to chemically change their orientation.
- While it's not exactly encouraged directly, the wizards of Discworld (who are forbidden to reproduce as a means of preventing sourcery) apparently are willing to tolerate homosexuality among their fellows.
- The Shore of Women, by Pamela Sargent. Men exist outside the walls of the central city, so the only relationships available are between women.
- From the New World uses the trope, but only among children and not for population control reasons. Instead, it's expected that teenagers below a certain age will have sexual relationships within their own gender until they're teamed with a student of the opposite gender "for schoolwork purposes," at which point they're permitted to enter into opposite-sex relationships. This is done because the fact that Everyone Is Bi is part of Kamisu 66's social control system, or as one infodump puts it, "the society of love."
- In A Brother's Price by Wen Spencer, heterosexual sex is allowed, but next to impossible for unmarried women, as men are so scarce. This leads to female prostitutes who try to appear as masculine as possible so attract female customers.
- The case in the kingdom of Vere in Captive Prince. Having an illegitimate child in Vere is highly stigmatized, so many pre-marital relationships are homosexual.
- In one episode of Barney Miller, a man claiming to be a time-traveller is arrested. He says that in the future (he doesn't specify when exactly), the government encourages homosexuality as a way of keeping the population down.
- The Onion, parodying opposition to same-sex marriage rights being billed as "protecting traditional marriage" ran an article called Massachusetts Supreme Court Orders All Citizens To Gay Marry