I think saying it's mass psychosis is ignoring the fact most people truly believe wrong and even really dumb things all the time. It's just now they've all aligned on one issue.

A bunch of healthy 30 year old teachers believing they are all going to drop dead of covid is really no different to a church full of people believing Christ is going to come back at any minute.

It's a really normal reaction to think these people can't really believe this stuff and there must either be something wrong with them or they are lying but actually it is a constant pattern in human behaviour.