But why would God give them perverse instincts? That they act by instinct is not an argument. You assume that sexual attraction is necessarily a high order rational process. You have not justified that claim. Evolutionary logic rather suggest that the mechanisms of sexuality are a lot more primitive, since they are required for basic sexual reproduction in species who reproduce in that manner.
God gave man a law and morality that is very different from nature.
To be honest, you're really asking a deep, fundamental question that I
could give my opinion on, but the fact that you're even asking it tells me you struggle enough with it to not be willing to accept an answer.
What scandal do homosexuals cause except for offending bigots?
God destroyed Sodom and Gomorrah because they were sexual deviants- anal and oral sex is an abomination to God, you see, and homosexuality is how Christians largely define the sin of those cities because the only way they can have sex is through those acts.
With anal sex specifically, a person carrying any illness may as well be injecting their partner with a needle, because that region of the body absorbs anything and everything.
By all of evolutionary theory, it ought not even exist- that's a bit of the irony of the whole matter: people who support evolution also tend to support homosexuality.
They are just conflicting agendas, both against the Creator.