The anti-gay contingent doggedly employs the notion that homosexual behavior is "unnatural" and, therefore, should be condemned. The pro-gay contingent often counters this by asserting that instances of homosexuality can be found in the animal world and that many, if not all, homosexuals are born that way and cannot change...And, therefore, homosexuality is about as natural as it gets. The pro-gay side often proceeds to assert that, in any case, nature is a mixed bag: some things in nature are good, some bad, and most things, most likely, are neither. So condemning a behavior "because it is unnatural" is inadequately supported at best, and seriously flawed at worst. Nevertheless, the pro-gay contingent commonly proceeds to make the very same mistake it has just critiqued: that BECAUSE homosexuality IS natural, it should be morally acceptable.
I agree that nature is a mixed bag. So I believe that justifying a behavior because it is natural is just as unsound as condemning a behavior because it is unnatural. These arguments "from nature" simply don't pass muster, and I believe the larger, ongoing debate on the moral acceptability of homosexuality would be better served if both sides dropped these lines of reason and proceeded on to more persuasive arguments.
I have issued a couple of challenges on this topic only to have my opponents disengage after the the first round, so I hope posting this opinion here will spur others to accept a debate challenge. I am more interested in exchanging opinions than in winning a debate, but I figure a formal debate on this topic would be a great way to interact, so please don't hesitate to contact me via this forum or my profile page.
To me, arguing about the validity of sexual orientation is as ridiculous as arguing about the validity of having red hair, living in Argentina, or having a passion for cycling. Aside from that, these arguments often commit the naturalistic fallacy, which equates moral value with whether something is "natural" or "unnatural" (such as using computers, driving cars, taking medication, or virgin births for instance?)
Those who have homosexual feelings don't need to justify or argue for them. If they are your feelings, and acting on them harms and victimizes nobody, they are valid without any discussion of nature. They are not logical or illogical, they just exist, the same as heterosexual feelings - and we would do well to honor them.
To be anti-gay, ultimately, is to be anti-"other people's private lives": it is about imposing a judgement on the feelings and orientations of EVERYONE else who experiences homosexual attraction - despite knowing nothing about the majority of these people, and never having walked in their shoes or experienced their unique situation. To me, this position is ridiculous for anyone who is not a mass-mind-reader.
Lets start.... Here a a full list of other things common in nature in terms of love <3
*Incest (So common that virtually every animal with a family has slept with a sibling and parent.)
*Polygamy (So common that nearly every Feline and Canine partakes in it as well as many others.)
*Sexual Cannibalism (You should probably look this up if you do not know what it is.)
These are very common, but we STILL consider each one immoral in our species. So being natural in other species doesn't necessarily define what's natural in our own species.
Homosexuality is actually highly uncommon. Being found in nature doesn't make it natural. Being common (or at least reasonably found) in nature does. You know what else is found in nature, but is considered unnatural?
*Albinism (Which is still consider much much more common than Homosexuality.)
*Extra appendages (Which, get this, is still more common.)
The reason it's so easy to find pictures of gay animals is because it's so uncommon that when one is taken, it makes the front page of every magazine and website. Now how many of these images are actually of partners or close friends, and not of a gay couple, is disputable, further lowering how common an actual gay couple is to find in nation.
Conclusion: Being natural in other species doesn't dictate what is considered moral in our own. Homosexuality is actually among the most uncommon (unnatural) things to find in nature, more so than Albinism.
But you generally don't see pro rights activists just randomly saying "animals can be gay so gayness is awesome." The point that homosexuality exists in nature is generally made in response to the factually incorrect claim that it does not. So generally speaking, I would say that it is seriously flawed when used by the anti-rights activists as a sword but not flawed at all when used by the pro rights activists as a shield.