The idea is that if your sexuality is not innate, then it can be changed. There's long been a desire to prove that homosexuality is genetic in order to counter the claim of bigots that they can turn people straight through shame and abuse.

It's frustrating on several levels. One, there is an element of the naturalistic fallacy; many people feel that homosexuality being "natural" (e.g. occurring in many animal species or being immutably determined by genes) is a strong defence of it (as opposed to the preferable argument of "it's not hurting you, so you have absolutely zero grounds to object to it"). Two, many people want to be able to point to a single gene as the causative factor, when genetics is rarely so simple, and other prenatal factors may contribute (e.g. something that happens during gestation).