Sorry I haven't been responding to posters comments. I found something interesting with what you said. You talked about how homosexuality appears in the animal kingdom.
I was watching a show on Discovery Planet on how some different animal species will kill and eat their young babies after birth.
So would it be natural if a human parent kill and eat their babies just how homosexuality is okay among the human species?
I know this wasn't directed at me, but I'll take a stab at it. We (as humans) tend to value life. Therefore the life of an infant is something that shouldn't be destroyed, especially once the thing has been born. There's obviously some debate on the whole abortion topic, but once a child is born, most developed countries have provisions in place to take the kid off your hands - you needn't kill it just to be able to avoid raising a kid, so most would agree that it's morally wrong to kill your own child.
I suspect that talking about homosexuality in the animal kingdom was less of an encouragement to look at animals to learn morality (animals kill each other in a fight for a mate, but we humans typically look down on that sort of thing, too) but it was an admonition to look at the fact that some animals seem to develop strong homosexual tendencies. Since these animals are not typically considered self aware, it would be hard to argue that they're making a conscious choice to be homosexual. This is an effective means of demonstrating to a heterosexual person that homosexuality in humans is likely not a conscous choice in all (or even most) cases. The point is, gays are often born gay - so why should they have to suffer due to something outside of their control? If they can find a way to be happy (i.e. find another gay partner) in a way that doesn't interfere with any unwilling participant's happiness, why shouldn't they?