Let me address the Greek issue. First, most Greek homosexuality depicted is between a older dominant male and a submissive adolescent male. Adult ma,es who had a homosexual relationship with other adult males were subjected to ridicule. Aristophanes mocked them on more than onr occassion. Most older dominant males also had wives, they were strictly homosexual.
The fact that the rate of homosexual activity varies among cultures does not prove that genes do not have a role. In societies where homosexuality is not repressed, as it is in cultures influenced by Abrahamic religions, there will be more homosexuality. No one argues that point. Genes only predispose individuals toward certain behaviors. They are not a final determinant of your behavior. I cannot point what in my upbringing led me to believe that there was something very attractive about Raquel Welch in One Million Years B.C. I was 9 at the time I saw the movie.
No one argues that diabetes is often hereditary in nature and can often be controlled through a proper diet.