I'm going to toss in my 2 cents here... although it'll probably be more like 25 cents by the time I am done...
First of all, back.sliden's question, though dumb as fuck, is one that I have heard before. Not put quite that way, but still... I work in the adult entertainment industry where you would think there would be a broader understanding of the wide and wonderful world of sex. And yet, I had an unbelievable time trying to make my account rep at the company that hosts my website understand that the gay audience isn't interested in seeing banners of women splaying themselves on my pages. His understanding was that, gay as we are, we're guys, so regarless of where we stick our dicks we still like pussy.
Bzzzzzt! Wrong-o
The argument came up a number of years ago on the Dr. Laura radio show (remember her???) about the unnatural-ness of gay sex. Her comment about homosexuals being biological errors sent a shock wave through the gay community because it felt as though she were attacking us at a core level. However, strictly biologically speaking, she was close to correct.
And here is where we differentiate between "natural" and "normal". It is not biologically normal to be homosexual when you consider "normal" to be "the norm", or how the majority of creatures on this planet behave. Approximately 90 percent of the human population (give or take) is heterosexual, making that unquestionably the norm. Therefore, homosexuals, comprising roughly ten percent, are not the norm and therefore biologically un-normal. Whether indeed that is a biological "error" or just the difference brought about by various combinations of biological factors is not really known.
But back.sliden, like so many on the side of the religious right (not that he is...), seems to believe that being gay is a decided behavior... something we homos wake up one day and decide to be. It is not.
As for "natural", two homosexuals engaging in sex, or any kind of romantic behavior with members of their same gender is no less natural as would be two heterosexuals engaging in the same behavior with members of the opposite gender. It may not be normal or natural for a heterosexual to engage in said behaviors with another of the same gender, but it is perfectly normal for gays to do so. And it is un-natural for gays to engage in sex with members of the opposite gender.
As was pointed out earlier, wearing clothes is not "natural". Nor, quite frankly, is wearing condoms during sex. Nor are many things we each do in our day to day lives, (including communicating over the internet) even though we may have grown accustomed to those activities and consider them "normal". So that which is natural may not always be normal. It's the way the real world works.
OK. There's my 25 cents. And for good measure I'll toss in this penny thought: back.sliden, you should USE your big head more for thinking before you post things rather than for just looking pretty.
BBJack