Well, homosexuality (although not gay marrige) was much more traditional in the Greek east then in the Roman west (where it had only become acceptable under Greek influince). And yet it was the west that collapsed.
Also, there was a great deal of internal conflict (of the general declares himself Emperor and marches on Rome variety) even before the conversion to Christianity.
Homosexuals are a small proportion of the population. Annoying them would not make them emperor popular, but banning pagan ceremonies would cause far more discontent, because they are a greater proportion of the population.
Coups tend to resolve one way or the other quite quickly, but religious conflicts drag on and are more personal to individual citizens.
The pagan customs were banned in 393. Rome fell in 410.
I'm not saying its the fault of Christianity. But maybe its a 'United we stand, divided we fall' situation?
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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