Christian vs. Christian After The Edict of Milan

Ramsay MacMullen's Christianity & Paganism in the Fourth to Eighth Centuries has generated unhappiness in some quarters, for it focuses on how Christians turned from persecuted to persecutors just about as soon as they could after Constantine and Licinius issued the Edict of Milan in 313 AD.  Even after the reign and decrees of Theodosius, paganism, Prof. MacMullen maintains, did not just just fade gently away.  Not even imperial blessing and official preference were sufficient.  To complete the job, Christianity and Christians had to persecute, and many did so with gusto:

It used to be thought that, at the end, the eradication of paganism really required no effort.  The empire in its waning generations had suffered a decline not only material but spiritual.  Of itself, "paganism had by late antiquity become little more than a hollow husk."  To replace it, only a preferable alternative was needed which, when supplied and explained, over the course of time inevitably found acceptance.  But historians seem now to have abandoned this interpretation . . ..  The real vitality of paganism is instead recognized; and to explain its eventual fate what must also be recognized is an opposing force, an urgent one, determined on its extinction.  Such a force is easily felt in Christian obedience to the divine commands of both Testaments, calling for the annihilation of all error.  It was this that controlled the flow of religious history from the fourth century on.

But I digress.  The point of this post is to highlight a single phrase that I find so startling that I can scarcely believe it, notwithstanding that it comes from the pen of Prof. MacMullen.  After the Edict of Milan, while Christians began to focus on external enemies (pagans, Jews, Manichees), at the same time

sectarian rivalries within the church continued unabated and with freer use of force, now that it was safe (so in the century opened by the Peace of the Church, more Christians died for their faith at the hands of fellow Christians than had died before in all the persecutions).