Early pacifistic Christianity was moderately workable in the context of the Roman Empire. Despite the "Christians to the lions" stories, if you paid your taxes and didn't try to openly undermine Roman authority, you could live your life in peace and relative security.
When Rome fell, you needed a class of people who could rationalize being Christian with the necessity to respond with extreme violence towards raiders, pirate, and barbarian invaders. These people became the feudal nobility, ruling over the rest who lived as serfs.
Drawing a line at which no enemy dare cross against your family and fellow Christians (without their consent) isn’t quite the same as keeping the serfs down. Fortunately God willed it that the Christians comprising the church, in the same manner as the Jewish race today, survive on God’s promise and not on lack of blunders or things that would be regretted in hindsight.