“It’s highly unlikely the Roman Empire declined due to homosexuality or even immorality...”
It did indeed fall due to homosexuality and immorality. Those Roman orgies actually happened. And the government promoted homosexuality.
Some historians have continued blaming the fall on the gays. Roberto De Mattei, an ultraconservative Italian author and professor, trotted out the idea as recently as 2011, saying the invaders were God’s justice visited on the queer empire. “The invasion of the barbarians was seen as punishment for this moral transgression,” he said on a radio show that year. “It is well known effeminate men and homosexuals have no place in the kingdom of God. Homosexuality was not rife among the barbarians, and this shows God’s justice comes throughout history.”