This is a dark one. I can understand why things like Scientology are popular from a primal sense. The need to be part of a group is fundamental to survival.
This can be dangerous when that group is malicious, wilful or not. Not saying Scientology is malicious – at least not to current or possible future devotees. For example the word genocide is a good example of how large numbers of complicit parties can perform pretty nasty things. So we can see plainly that people in general can hold beliefs that can be harmful to others…
I don’t like to talk about this due to it being so definitively polarised, but an example today I think could be vaccines…
Others may be Prison Unions in the US, the war or drugs, or more generally the proliferation of industrial corruption.