The tie that saved Rome. Do Western nations need a State Religion?

[The Mikado]

The failure of historicity here is amazing.

First, Constantine did not establish a state religion in Rome, Theodosius did seventy years later.
Secondly, none (and I do mean none) of the problems of the Tetrarchy era were caused by the multiplicity of gods worshipped in the Empire.  The only religious tension that existed was between the state and Christianity, or to a lesser extent, between the state and Zoroastrianism/Manicheanism, and in the former case, it was a question of patriotism first and foremost (Christians are unwilling to pray to the Emperor as a God or worship at the Altar of Victory: does that mean that they hate the Emperor and oppose Victory?).
Thirdly, In whose crazed, fevered imagination did the institutionalization of Christianity help Rome in the short term? It would eventually become a pretty solid foundational bedrock of the Eastern Roman/Byzantine state, but to get there, it required nearly three hundred years of violent purges, counterpurges, and doctrinal disputes (can't get to One Emperor Ruling One People Under One God without suppressing all the people with varying ideas of that One God that might undermine the One Emperor part). The doctrinal disputes destabilized the Empire consistently for three hundred years and only really stopped doing so after the rise of Islam and the fall of all the heavily Monophysite areas like Syria and Egypt to the Caliphate, leaving the Romans de facto spiritually homogeneous through loss of the heretical areas.