This is a question for those who have a mostly negative view on the whole issue of Constantine the subsequent Constantinian shift within the Roman Empire towards Christianity. Many have a negative view about this history and I think it would be beneficial to ask two questions:
Why was it a mistake or mostly a mistake for the Church to associate with the Imperium?
Then the follow up would be:
What should the Church have done instead?
I think it was one of those things that was meant to be, possibly inevitable-which nonetheless resulted in a learning experience: that it's important that the church is disassociated from any direct involvement in the government.
But...at the time it seemed as if heaven might actually be realized here on earth, a reasonable enough hope or expectation even if it seems naïve now. But Christianity had brought an extremely stabilizing force into a very chaotic and dark and warring society and world-and the Church was the one link that could and did bring feudal enemies, for example, together-on a moral basis. Also, the Edict of Milan which Constantine helped draft was for the purpose of legitimizing
all religions and ending religious persecution, even as he favored Christianity itself. And his presence did not influence the Church's teachings as is evident by the fact that the Council of Nicaea, which he was instrumental in getting convened, ruled against his own pet belief in Arianism. And the teachings of the church in the west would continue to be conservative and orthodox if one seriously looks into the teachings, such as the councils following Nicaea, for example. And in any case the change allowed the faith to be spread on a
much larger scale.
Either way, the church and civil government became strange bedfellows, which is as it should be, but for awhile it was looking as if some temporal power might actually be God's will for the Church. Heresy was looked upon as an absolute danger to the stability of a society which had become enlightened to a large degree by a religion that had placed hope and love and goodness and order and eternal life at the foundations of a world that was more often experienced as evil and dark and selfish and meaningless and chaotic and hopeless- and just a giant slaughterhouse at the end of the day. We can't even identify with that life now even as we may seem to be slipping backwards increasingly, into atheism. And those positive basics of this new religion remained regardless of how well or how poorly its people and/or leaders were heeding its message at any given time-while, to be fair, there have
always been many, many who took the message of love and brought great progress with it to advancing God's kingdom in one manner or another.