There is a difference between the Church and terrorists who call themselves Christians, it's the same difference now as it was then. I would suggest that you bear that in mind when discussing these things.
as far as Constantine goes, I think he had an interesting idea, using a hybridisation of the popular civilian and military religions to try to hold the Empire together, and in fact it sort of worked, if you look at Mediaeval Christendom and the Papacy you can see that it helped to hold the Western powers at least loosely together in terms of language and culture.
Unfortunately the Empire was already in terminal decline when Constantine took power and he was unable to find a successor who could continue things in the same direction. Change of direction was a major issue for the Roman Empire, and the Republic before it.
As a man he was pretty ruthless and dispicable though.
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