Nature+Nurture=sexual orientation.
Clearly sexual orientation isn't a binary thing. You have 2 extremes strongly hetero and strongly homo and you have everything in between. Smack in the middle is true bi-sexual. The bell curve is skewed to the hetero side of the bisexual middle so that there are many more people that are moderate to strong heteros vs moderate to strong homo.
Where you have a continuum for a psychological state it means the influence of multiple factors in determining the state of any given individual. Genetics is a part of it, but I'm sure it's not the whole story.
So, the curly question for the liberal minded is, given the multifactoral causation, is homosexuality largely preventable if the major environmental (nurture) factors are influenced towards the hetero outcome? Should research into causation be banned? While people remain ignorant of the true causation in individuals the idea of prevention (or even treatment) cannot come up in public discourse. But as soon as someone does the research and identifies key trigger factors treatment and prevention (or induction) becomes something people will want to do. Imagine: the pink pill causes homosexuality in male foetuses and heterosexuality in female foetuses, the blue pill does the opposite. Should such pills be allowed to exist? What if an existing product, like say caffeine free diet coke causes gayness and normal coke causes straightness when consumed by pregnant women? What if men eating oysters in the days leading up to the sex act causing pregnancy leads to gayness (or at least a significant increase in the chance of homosexuality in the child)?
It's really not the cause that's important, it's what you do with the information once you identify the main causation factors.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix
