How a priori reason do you want it to be? There's at this point a general consensus that sexual orientation, while culturally mediated, has a large genetic component. I don't think that anyone thinks there's say a gene for Christianity or the like. And while self-identified sexual orientation can change, that's substantially less common an occurrence as changes in one's religious self-identification. For example, in the US about half of all adults have changed their religion at least once in their lives. See here. Some of those people are people changing f... (read more)