I imagine most people kind of knew what happened in those camps but there was just enough distance between them and the actual suffering that they could ignore it. See the people calling for less immigration or sometimes actual deportation; those immigrants will suffer for it but the people calling for it will not see that suffering. See people eating animals; most could never put a live chicken in a blender or a pig in a gas chamber but since they are just far enough away from the act they don’t mind supporting it.