I have never heard anybody say that homosexuality is completely innate, it is most likely not. Take another example like heart disease, pardon to any homosexual that may be offended, it is widely supported in the scientific community that your genetics determine the RISK for heart disease and your environment is what actually causes it. However, in the case of homosecuality the organ that is in question also happens to be an amazingly complex chemical computer that is WAY beyond the grasp of our sciences to this day and for many generations to come.
As for homosexuality being immutable, it most likely isn't in all cases. In fact my girlfriend is an example of somebody who at one point was attracted to women and if we ever part ways, I'm sure that she may find herself in relationships with other women. In fact, bi-sexuality is most likely a person whos attraction to others easily swings both ways and is in essence quite mutable. Ancient Sparta exemplars a place where most males practiced frequent homosexuality due to their constant lives among other males while at the same time they headed a household. This proves that hetro-sexuality is also mutable. Lesson: people CAN change.
Also imagine this: you are left handed, a purely genetic situation, but you are forced to write with your right hand. You CAN do it but studies show that is causes many neurological defects and harms their mental health to do so. In most cases it would be quite painful for a homosexual to practice hetrosexual life and would simply make the person being forced to change unhappy.
And beyond that, what kind of person would purposely go against all of society, endure criticism and riducule, risk assault and more just so they could have a romantic relationship with somebody of the same sex if they didn't feel that it was something they couldn't change?
Aineo- you are the exception, not the rule.
http://www.theatlantic.com/issues/97jun/burr2.htm -One note is that the writer is gay so there may be some bias in your eyes. In mine, I think he just wants to know why he is different.
The major reason why you haven't heard any definitive scientific proof is because the Scientists have not a clue what they are looking for and every time they think the have found something, it doens't pan out. That, however, isn't proof that homosexuality is mutable, it just means we don't really know either way but from physcological research have found that most homosexuals are always homosexual.