In cults, members are prevented from contact with the outside world. When you control the flow of information that is what what you’re doing; you are preventing members, or in the national sense citizens, from making informed decisions about the world around them, and that denies free will. This is a totalitarian concept. That isn’t just what Hitler would do, but what he pioneered on a state level.
Why is this relevant? for a whole lot of reasons… illegal psychological operations including social engineering, social conditioning, black propaganda, and "unofficial cover."