o If you believe in evolution, then it would die out.
- Homosexuality arises from heterosexual couples all the time, so any genetic component would likely be a predisposition or a complex inheritability rather than Mendelian (note that this does not preclude homosexuality being innate and/or fixed!), lowering the selective pressure against it considerably.
- Kinship selection. Since blood relatives other than one’s own children also share genetic material with you (parents and full siblings being equivalent to one’s children, grandparents, parent’s siblings, singling*s children and half-siblings equivalent to one’s grandchildren, etc.), there can be evolutionary benefit to forsaking one’s own reproduction. For an extreme example, see eusocial insects.
- Homosexuals are still capable of having sex with people of the other sex and having children. Especially if their culture rejects homosexuality as valid, perhaps even outlawing it… In other words, congratulation, homophobes, if there really is such a thing as a “gay gene”, you’ve helped it spread!
o If you believe in a God, then God said it is wrong and it should die out.
The God of the Bible is not the only Higher Power worshipped by extant mainstream religions, let alone the only Higher Power imaginable. A non-homophobic Creator is entirely conceivable.
Male and Female, of any species, have specific parts to create the next generation to continue.
Not all species have males and females. There are many that are simultaneous hermaphrodites, as well as species that reproduce through parthenogenesis - although lineages where sexual reproduction is lost entirely are inevitably shortlived (in evolutionary terms!), many groups that primarily reproduce asexually with sexual reproduction taking place only under specific circumstances, usually stress-related, are very successful. And then there is the New Mexico Whiptail, also known as the “Lesbian Lizard”, who are an all-female species of lizards that produce through parthenogenesis, but still need to simulate mating with each other to trigger ovulation.