The source of pretty much all of the bad ideologies in the world today is the belief that groups comprising millions of people, all over the world with radically different backgrounds, thoughts, beliefs and motivations are a big monolith who are all doing and thinking the same things. This fallacy is midwit cope for people who are incapable of handling the incredibly complexity of the world and need to break everything down into incredibly reductionistic problems, solutions, and villains, when absolutely nothing in the world is simple.