We can always use more case studies of insanity that aren't religion, right?
Well, Miracle Mineral Supplement is my new go-to example for Bad Things happening to people with low epistemic standards. "MMS" is a supposed cure for everything ranging from the common cold to HIV to cancer. I just saw it recommended in another Facebook thread to someone who was worried about malaria symptoms.
It's industrial-strength bleach. Literally just bleach. Usually drunk, sometimes injected, and yes, it often kills you. It is every bit as bad as it sounds if not worse.
This is beyond Poe's Law. Medieval blood draining via leeches was far more of an excusable error than this, they had far less evidence it was a bad idea. I think if I was trying to guess what was the dumbest alternative medicine on the planet, I still would not have guessed this low. My brain is still not pessimistic enough about human stupidity.
Whether you change beliefs in response to a new case will depend on the nature of the selection or sampling process . If you go through a history of quack medicine, you'd get lots of new case-studies but you might not change your beliefs about typical human epistemic performance at all.
Even if new cases are selected to be examples of human stupidity, they might still be roughly random within that class. So cases that are more extreme than one's expectation will shift your beliefs. But this might leave your beliefs about the frequency of incidence of human gullibility unchanged. (Maybe I come to think that believers in quack medicine are even more stupid than I previously thought, but not that such believers are any more common).
It's very hard to judge whether one's new information is selection-biased in some way. In areas like psychology and political science, it's not so hard to find academic papers that support either side on a debate. Even if you can't find that, it could be because of file-drawer effects or because of topic has not been investigated much by academics.