"Historians might consider the decline of Rome as partially related to a societal loss of morals and widespread homosexual behavior condoned during that period."Historians DID make the above conclusions. That's a well-known fact.
Yes, but the historians were talking more about a decline of civic responsibility than of private morality. It wasn't so much private vices in themselves, it was that they got in the way of public obligations and responsibilities. Earlier Romans hadn't been models of virtue in our sense, but they kept their impulses under control enough to conquer and rule a large part of the world.