There’s nothing that conclusively proves it can’t be both/and. People can choose sick or “diseased” ways of thinking, with various amounts of ignorance involved about what is normal. To the extent that people in the process of doing so willfully reject God’s light about what is right, sin is implied. And the august scientists of NARTH have found that just about any plausible cognitive theory of homosexuality is equally useful to caring therapists helping willing patients break this habit, further clouding the picture. In a way I would have to venture that this is much like God, who “gives wisdom without finding fault.” God is not interested in blaming a person, at least not a saved person, for a past whose sin has been confessed. God is interested in showing that person what the right thing to do is.
Well, of course. Sins of all sorts corrupt body and mind and soul.