I am very tired of hearing that Our Lord's Church regards homosexuality as a sin. Let's be clear--as a result Original Sin and our fallen, wounded nature, we are afflicted by all kinds of disorders that are not of our own making—physical, mental, emotional, sexual, you name it. In Catholic teaching, what governs whether something is naturally disordered is whether or not it is working according to its proper end, whether it is properly ordered to its natural purpose. If it is not, we call it “disordered”. Inclinations with respect to any of our faculties which make us want to use those faculties in a way inconsistent with their proper end are not sinful; they simply reflect our own disorder, our lack of perfect integrity.
Such predispositions often become major temptations, and if we continue to indulge an inclination to act in a manner inconsistent with the relevant proper ends, we sin. The Church does not hold a homosexual inclination (orientation) to be sinful—it is merely disordered—but the Church does regard homosexual activity as sinful, in keeping with the clear witness of Scripture, Tradition and the Magisterium.