Morality (much like all of behaviour) has an evolutionary origin. For this reason, I think the only things that we can even begin to call objectively immoral are things that are evolutionarily disfavoured.
Oh, like homosexuality! Cool. I was looking for a reason to hate those guys.
Do you honestly believe homosexuality is necessarily evolutionarily disfavoured?
That's my thinking at the moment. I'm open to convincing if you want to try and sell me otherwise, though.