My very liberal world history teacher once taught me that the Roman empire declined, in part, because of rampant homosexuality.
Just three decades ago, people of all political persuasions agreed that is was a perversion.
The problem with this theory is that Nero killed himself in 68 AD. "Rome," the western empire, fell in 476, more than four centuries later. It's difficult to draw a logical effect from a cause more than 400 years earlier.
It's like blaming the collapse of the US on something King James I did.
The greatest days of the empire were well after Nero.
It should also be remembered that the Roman "historians" apparently made stuff up with great freedom. Nero was almost certainly a bad man and emperor, but it's unlikely he's guilty of everything he has been accused of.
The difference is that then, Nero’s antics didn’t affect much outside the city limits of Rome. Nowadays, our decadent emperor hiccups and the whole world gets Ebola.
Funny, my very libertarian economics instructor taught me that the Roman empire declined, in part, because of currency debasement.
I suspect it doesn't matter which one of them was correct as we are getting both in spades.
They also overextended their empire, started using mercenaries and got away from the professional soldier.