Is murder wrong because a magic book says that it's wrong or is it wrong for deeper reasons?
If your only justification for homosexuality being wrong is based on the the magic book telling you so so then you're simply going to be left behind as an arcane vestige of vapid rigidity while society, much more adept at focusing on fairness, caring, and social justice than any of the models presented in the magic book, distances itself from all of these ill and pre-conceived assumptions of right and wrong.
The very concept that society, or rules, or laws, or basically anything at all is stagnant and unchanging is just absurd and an insult to anyone who studies sociology.
Homosexual behavior in animals - Wikipedia, the free encyclopedia
Also
Normality (behavior) - Wikipedia, the free encyclopedia
Oh, and this one too
History of homosexuality - Wikipedia, the free encyclopedia