I think that a relatively sane viewpoint would cover the idea that being black is not something the person chooses to become, while engaging in homosexual behavior is very clearly a lifestyle choice; given that there is genetic coding for whether you are black or not, but no coding for homosexuality.
While there are many choices that all people make in the sphere of sexuality, choosing who lights your fire is not one of them. I can no more choose to find men sexually attractive than I can choose to not find sugar sweet.
I have no way to answer that without resorting to anecdotal evidence, as you are yourself doing. I could answer with quotes from the "ex-gay" movement ... but those are anecdotal as well.
I don't think there is a way to gather hard evidence without engaging in unethical conduct (that is, any psych experiment that would give data might irreparably harm people and thus would be wrong).
