Conspiracy Mental Issue

Family member believes earth is flat. There are no planets. Deep state conspiracies. All Telescopes have images of fake plants. Tom Hanks and other celebrities are under house arrest and pedophiles. The Tom Hanks in movies is an imposter. Any many more beliefs etc…… too many to list. Also refuses to watch movies about space because all lies. I have stop discussing with this family these beliefs because it gets heated. Even if I have proof. I just don’t go there or try not. Besides, I don’t know what is secretly happening according to them. They have more insight. In the past they were never like this.

Question: I know there are others like this - Including a coworker. So, what is going on global with people like this. Why do they start thinking like this ? What is the root cause ?

I guess, that people, to which the world becomes overwhelmingly complex, just wish to simplify things, so that they feel, they have control over their surroundings again. Plus: It may give a boost to a probably low self confidence, to believe that one has insight into hidden truths, that most normies will never get to lay their hands on. And last but not least: such beliefs may grant one with affiliation to like-minded communities, which couples with a feeling of belonging to a superior group. I don't think yet, that this alone is a mental health issue, but just a — yes, strange and worrisome — "normal" coping strategy.