I'll start with the British Medical journal
https://pubmed.ncbi.nlm.nih.gov/17146141/So far no one seems to have recognised its evolutionary role.
The survival value of homosexuality for the human species is to be found in its effect on population growth. Anyone who is worried about environmental degradation caused by the growth of the human population should promote homosexuality. Indeed, it would be desirable if most people became homosexual and only a small, selected proportion of humans of every recognisable subgroup attended to the modest reproductive needs of the species.
All the effort, emotion, and money spent on family planning could be saved, and disgusting and unnatural practices of contraception—such as genital mutilation, various prophylactic methods, and even withdrawal and the observance of cervical mucus—could be done away with. Indeed, homosexual sex is akin to organic farming inasmuch as it eschews artifice, yet it yields pleasure and elation and, often, pure love.
The ideal social organisation of mankind in this overcrowded world would be one in which the majority lived in homosexual monogamy. If homosexuality became the norm, population numbers would decline precipitously.
From the point of view of the species, the survival value of this arrangement is obvious. The concept of cultural evolution can explain how the paradigm leap came about, for so far “natural” evolution has been known to work only through the machinery of reproduction and not its negation. Avoiding reproduction is a cultural activity par excellence.
As far as recruitment into the breeding groups is concerned, in the immediate future there will be no shortage of volunteers. But eventually, as the breeders will become a minority, there is the danger that they will be discriminated against. Protection of “aberrant” behaviour such as reproduction will be just as much in the interest of the species as is now the upholding of homosexual rights for the sake of reversing population growth.
Prejudice against homosexual marriage will diminish as soon as people realise that that newly established institution is a guarantor of “natural” population policy.