I don't see how that is in any way obvious. Nor is it obvious that homosexuality is aberrant in the animal kingdom -- in fact, the available evidence argues to the contrary. In many primates, most notably bonobos, sexual release has a social bonding function quite separate from reproduction.
There's a pretty credible argument, based on animal studies, that there are selective pressures in favor of homosexuality. Incidences of homosexual behavior among animals tend to increase when overpopulation kicks in. Populations without latent homosexuality will tend to overbreed and overfeed until they all die out, while populations with that latency will find their own form of population control and survive.
The reality is that we are born with a genetic drive to heterosexuality - and only psychosocial trauma during development powerful enough to derail that drive (ie, molestation) brings about homosexuality.
TWEEEEEEEEET! Flag on the play. Using the conclusion as a premise to prove the conclusion. Ten yards and loss of down.