Becoming a niche is a third possibility if ideas are suitable to one area but hard to expand to different areas.
I do think rationality is a niche. I had a conversation with a not-particularly-bright administrative assistant at work where she expressed the teachings of Jehovah's Witness as straightforward truth. She talked some of the chaos of her life (drugs, depression) before joining them. As I expressed the abstract case for, essentially, being careful about what one believes, it seemed clear enough to me that she had little or nothing to gain by being "right" (or rather adopting my opinion which is more likely to be true in a Bayesian sense) and she...
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