You stated that Christianity retarded progress, was inimical to human flourishing.Never said "uniquely evil."
If that's true, you have to show history would have unfolded in a superior way if Christianity were just removed from the historical record.
Things like slavery and sexism were almost universal in all historical civilizations. If anything, the Romans, Greeks, and Muslims were worse for institutional slavery on balance than the Christian civilization that replaced it, or coexisted with it. I don't see how Christianity made the situation worse.
Now, in my opinion it's fair to give Christianity low marks on tolerance, largely because it's an exclusivist religion.