It is as though in the space of ten years we had slid back into the Stone Age. Human types supposedly extinct for centuries, the dancing dervish, the robber chieftain, the Grand Inquisitor, have suddenly reappeared, not as inmates of lunatic asylums, but as the masters of the world. Mechanization and a collective economy seemingly aren't enough. By themselves they lead merely to the nightmare we are now enduring: endless war and endless underfeeding for the sake of war, slave populations toiling behind barbed wire, women dragged shrieking to the block, cork-lined cellars where the executioner blows your brains out from behind. So it appears that amputation of the soul isn't just a simple surgical job, like having your appendix out. The wound has a tendency to go septic.

I don't see how this brutality was lacking when humans were more religiously observant. Furthermore, the quote seems to argue for religion.

Meaning the conclusion and the conclusion's reasoning are both wrong.