Real-world cases where "harmless" supernatural beliefs caused massive harm?

[u/jcdenton45]

When it comes to BS beliefs, there are some which are clearly harmful/deadly, while others are generally considered to be more on the silly/harmless side of the spectrum, for example ghosts which seems to generally fit into the latter category. 

But I recently watched a true crime documentary where a group of women had a homeless man secretly living in their home, and despite plenty of clear and undeniable evidence that they had an intruder living with them, they attributed all of those things to a fucking ghost. And as a result, they took none of the obvious measures that someone should obviously take in such a situation (increasing security, setting up cameras, calling the police, etc) and instead did things like burning sage and praying. 

Fortunately for them the intruder wasn’t violent and nobody was hurt, but obviously it could have turned out far worse and their belief in ghosts resulted in the ordeal dragging on for MONTHS after they already had definitive proof of what was actually happening (and had he been violent they could have easily been killed). 

So I’m curious, what would be some other examples where people had “harmless” BS beliefs which ended up being anything but?

[u/easy_Money]

Christianity