I have for many years maintained the position that there are two problematic streams of thought about Constantine that I've seen:
The one promoted by various Restorationist and Primitivist sects in which Constantine is a diabolical villain working to overthrow "True Christianity" by mingling it with Paganism and introducing a false religion that existed until the Reformation. This is stupid and obviously false.
Then there is also the view that Constantine was effectively all good, and that the coming together of Church and Empire was a good thing; that the union of ecclesiastical and temporal power is good. I think history is sufficient in demonstrating just how wrong this position is.
So therefore, what do I take as my position?
Constantine was a complex human person, and it is impossible to know all of his thoughts or what was in his heart. Was his conversion to Christianity genuine? I have no idea. Constantine did good things and Constantine did bad things. For example, Constantine's murder of Fausta and Crispus is obviously bad. Ending the persecutions against the Church? Good. Throughout his reign he both acted as Pontifex Maximus of Roman pagan religion; but he also granted Christian clergy the same rights and privileges under the law that was afforded to pagan priests. Constantine personally sponsored the building of churches and the printing of Bibles.
Constantine did good by calling together the bishops to meet and address the Arian controversy at Nicea; but Constantine did bad when he went against the Council of Nicea's rulings and deposed and exiled St. Athanasius the Great and had the heresiarch Arius placed on St. Mark's seat. Constantine in his later life sided with the anti-Nicene faction, and was eventually baptized on his deathbed by the Arian heretic, Eusebius of Nicomedia.
Constantine's legacy is complicated and messy. His successors, Constantinus and Constans were themselves split between loyalties to the Nicene and Arian factions--with ultimately Constantinus' Arian predilections winning with the death of Constans. Continuing the wound in the Church, and the struggle between Athanasius and "the world" for which he is remembered for his many forced exiles--Athanasius contra Mundum.
But it wasn't under Constantine that Church and State truly came together, that would not happen until the reign of Theodosius I, a devout adherent to the Nicene confession, and also the one responsible for bringing together the Council of Constantinople to reaffirm Nicea and address the Macedonian controversy. Theodosius also signed the Edict of Thessalonika, which made Christianity the official state religion of the Roman Empire.
It is only after Theodosius that we see the fruits of this. Only six years after Theodosius' edict Priscillian, a heretic, was put to death by the state.
It is in the context of Church-and-State that the worst things perpetrated in the name of Christ have taken place: the execution of heretics, Jews, Pagans, and other non-believers. Pogroms, crusades, inquisitions, witch trials. From late antiquity until quite recently in modern history the marriage of Church with the temporal powers of the world has frequently been the catalyst for many evils which were, horrifically, done in the name of Christ. These are historic sins of the Christian Church.
I say they are the sins of the Christian Church, because I reject the idea that this was a "false church", it was very much Christ's Church that either bore responsibility directly through action, or indirectly by being complicit.
Real Christians did really bad things. That is as much part of our history as anything else as Christians living today. And it's something we have to own up to. Even if it wasn't "my church" that is really beside the point.
Those who claim a great apostasy or some other nonsense want to cast blame to "those others" and wash their hands; the problem of course is it doesn't work that way. And, by the same token, those who champion these things seek to justify evil in order to try and avoid criticism against the Church.
But the Church, our life-giving mother in Christ, is not above reproach. With eyes open, with humble hearts, with contrition, and with many tears we must confess our sins and seek to walk humbly with our God and pursue kindness, gentleness, mercy, and justice as Christ's people in this world.
-CryptoLutheran