This example came to mind also.

I came across a woman last year in 'net chat who said she'd fallen victim to the Px paranoia as well. A certain someone advocating a Px doomsday had told her that she could see Planet X lurking close to the Sun by poking a small hole in a piece of paper, holding it up in front of her face, and looking around the disk of the Sun for the alleged inbound interloper. Unfortunately, she said she didn't know any better and was concerned enough to do so... and ended up with permanent retinal damage in the process.

Possessing beliefs (even really odd ones) is one thing, and not necessarily bad; promoting nonsense which might cause harm to others is beyond reproach.