Someone who actually lived under Nazi rule like Simone de Beauvoir during WWII bandying around the term "sub-human" makes her sound like a slow learner. But let's unpack this lowest stage of humanity. If the sub-human's main attribute is apathy, that means they don't care what happens to them. Then why can't others who do care about what they are doing just use the hell out them? If they want a routine, why not give them one building your magnificent palace or flipping burgers in your restaurant? If they are following a mindless herd, why not drive that herd into your corral? If they don't care if they are oppressed, you can't oppress them.

In Paris during the 1940-44 occupation by the German Wehrmacht and the Gestapo, most French people hated the Germans, who were ordered to be law abiding and polite, much less than the French men and women who collaborated with them. The collaborators came from all strata of society, and after Paris fell to the Allies many of them were dragged into the woods and summarily shot. Women who had German boyfriends were publicly humiliated and exiled. Most of the collaborators didn't have any ideological reasons for following the fascists, they just wanted regular meals and cigarettes. Those might be the sub-humans de Beauvoir alludes to.