The entire existance of Annihilationism. Think of an ideology that makes the existance of Anti-natalists in OTL look like the most centrist take possible, now add to the fact that many followers are either deranged Social Darwinists, people who will use the Atomic Bomb en masse and are climate doomerists and you have essentially the most uhinged group of Misanthropes in existance. Made even worse by the fact that they all appear in a considerable ammount of influence within the population in many places, England for example, where their proponents most democratic approach is the sterilizarion of their own population to avoid creating a new generation of human beings.
The break up of the United States is this as well, to many it was simply just another day in their lives except for the fact that an upopular politician got elected as president. Except that this time, people took up to the streets and were later joined by the Lion of Socialism, a man so insane that his introduction has him "chopping the head of a National Guard soldier with a fireaxe" and then everyone started shooting each other.
