There is no "homosexuality" in animals. The entire concept of homosexuality is made up by humans. Your article you keep quoting proves that. Yes animals engage in what we humans might call "homosexual" activities. But the actual act of sexual intercourse is for the sole purpose of reproduction. No animal species can thrive on an exclusively "homosexual" lifestyle. Therefore the concept of "being homosexual" is made up by humans.'
What do you mean by homosexuality here? If you're not referring to activity, then would you accept a lifelong same-sex attraction as homosexuality if it happened among animals?
Second you quote all these animals that do these activities but none of them are remotely close to the human species. The article clearly states it is DOMESTICATED sheep that engage in the activities. These are animals that have been taken from their natural environment and bred to be food. This is an abnormal activity in an abnormal situation. The entire event of the dolphin orgies ends up with the females getting pregnant, therefore the dolphins arent homosexual either.
Here is the definition if homosexuality:
Homosexuality is a sexual orientation characterized by esthetic attraction, romantic love, or sexual desire exclusively for another of the same sex.
No animal does this. Not one
This is actually not true. There are several species in which males have been known to form lifelong homosexual relationships, or only homosexual relationships their whole lives, and most of these have not been domesticated by humans. Wild geese, bottlenose dolphins, and albatross, to list a few, have all been documented in lifelong, homosexual relationships or lifelong homosexual attractions.
Studies have also shown that being gay could be genetic. And as with every genetic change or difference among a species. If it is an advantage the trait will prevail and pass on to more of the species. If it is a disadvantage it usually dies out or goes dormant within the species. If humans didn't have science to help homosexuals reproduce than they would die out because they can't reproduce. Yes the genes might pop up over time but in no way are they useful or sustainable within the race.
There is most probably a genetic element to some cases of homosexuality, but it can't be genetic alone, because the genes they have identified so far that show up more among gays show up among purely heterosexual men, too. Also, even if all gay people never reproduced (and most don't,) gay people would still be born at the same rates. They come from us heterosexuals, not from each other, and they haven't died out despite being around since the dawn of humanity (and before, as has been shown with other species.)
As for your survival argument, I don't think it makes sense. There is no single goal of life, only tendencies that exist strongly in most organisms, so usefulness isn't a lens that you can use to analyze all behaviors without ending up in functionalism (saying that everything we do is connected to survival,) which is illogical. There is no clear reason to moralize or politicize those tendencies- reproduction isn't inherently good or bad unless you introduce transcendent morals, which usually come from religion, and are thus unconfirmed and impossible to prove one way or the other.