The most useful of all the many good concepts in "Screwtape" is his idiom for a phenomenon I was already aware of even before I became a Christian. Living through the hippie era and what followed it, I could easily see how people "guarded against" non-existent or no-longer-current evils, while refusing to see ACTUAL PRESENT EVILS. Thus, with Nazi Germany long gone and the Soviet Union still up and running at that time, novelists and screenwriters STILL INSISTED on ignoring actual Communist brutality, while pretending over and over and over and over and over that the Nazis were coming back any minute.
This is the form of willful stupidity that Lewis, through Screwtape, cleverly described as "rushing about with fire extinguishers when there is a flood, and crowding to that side of the boat which is already nearly gunwale under."