You are spinning the word "lust". Predisposition -- sexuality -- is not yet lust. Lust is a decision. Thus understood, it is indeed sin (except maritally).
Perhaps. However I don't excuse homosexuality as a preference.
"Lust is a decision."
Job 31:1 "I made a covenant with mine eyes; why then should I think upon a maid?"
Heb. 12:1, "Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us,"
In both verses the idea is not to look at another woman if looking is not yet sin but a weight, a weakness that could become sin.