If you could get cancelled for teaching false things, there would be scarcely a professor to offer a theology class in a Catholic university. But as a matter of history, his assertion is hard to believe: Rome was overflowing with nonconsensual homosexuality from the days of its founding. As a matter of Catholic thought, the Catholic position is that the Roman Empire didn’t so much as fall, as it was supplanted by Christianity: instead of politically conquering the Barbarian tribes as Rome did, Christendom converted the Barbarians; the Barbarians defeated Rome militarily piece-by-piece, but in doing so, became no longer Barbarians. Eventually, Christendom became dominated in the West by various Catholic kingdoms, none of which were part of the Empire, but all of which had become “Roman”; in the East by the Orthodox Church and the “Byzantine” Empire; and in the South, the Gnostic and Arians who later became Muslims.
Reading a bit more on this, I see the point beign made: It’s not so much that homosexuality caused the collapse of Rome, but that Christianity’s incompatibility with homosexuality caused the collapse of Rome. I’d argue that THIS is correct.