Similarly, India had an extensive caste system for well over a thousand years, with very strict rules about social relations between castes. This was so "normal," that it was never even questioned. Does that prove the caste system is beneficial or "natural" or preferable?
Or not.That is the theory of evolution. Considering homosexual couples cannot naturally conceive children with third party participants, it is fair game to say that heterosexuality is biologically necessary for survival while homosexuality is not. That would be a fact. Just something to think about.
Homosexuality is found throughout the animal kingdom; it's been observed in over 1500 species already. Homosexuals can in fact reproduce, just not with a sexual partner of their preference (obviously). The plumbing still works, y'know.
Social relations are extremely complex, and suggesting that one particular behavior is somehow a "problem" is somewhat naïve.
In addition, the vast majority of human activities these days are not "necessary for survival." Including participating on web forums on the Internet.