There is nothing "unnatural" about being heterosexual
I guess it depends upon one's definition of natural to begin with. I guess I'm using Encarta's definition #6: "innate: inborn, rather than acquired".
My contention is that if -- and I realize that is a big "if" to you -- sexual orientation is genetic or even only congenital, then it is by definition natural, no less so than Downs syndrome, dyslexia, inborn immunities, or baldness are natural.
So from my perspective here is nothing "unnatural" about any sexual orientation.