If homosexuality was a mindset you'd simply decide whether to follow it or not; which obviously isn't the case as homosexuals are even today murdered just by their condition and won't change their mindset in order to "choose heterosexuality".
And no living organism is as simplistic as "it's genetic or not"; genetics interact with tons of factors and you can't simply say something isn't genetic.
my brother once told me that recent studies indicate that sexual orientation is defined during gestation. twin brothers usually have the same sexual orientation, while this same pattern is not found in conventional siblings or parents and their children, so its not genetic.
he announced that he was gay to our family at the age of 19, but he told me he had known all his life, he just didn't have the courage to admit it. so it makes sense to me that sexual orientation is already defined when a person is born.