I would add The Lord of the Flies, which is in fact a horror movie and all the more so because it’s based on facts, to that list. The 1963 movie version is a true and most important classic which was WAY ahead of its time. In the story a group of young schoolboys stranded on an island quickly divide into a secular/rational group and a religious/fascist group; the religious/fascist group eventually starts killing members of the secular/rational group.