Rome\'s 3 biggest mistakes.

[M. Demetrius]

As I see it, by the time the Empire broadly embraced Christianity, albeit in a perfunctory manner for the most part, it was already in decline, mostly because of Wander's 2 and 3 reasons above.

Add in to that the excessive taxation of provinces, leading to disgruntled populace there, necessitating more troops to keep order...and that the free food and games mentality in the core of the empire didn't add to production, and you have a recipe for disaster, regardless of choice of religious expression.