For some people (and I used to be and sometimes still am among them, though I’m trying, folks, I’m trying every day) a certain amount of social status and personal identity is bound up in hte ability to be “right” about stuff - to be the person who Knows Most, or who knows the Right Way.
A good example of this is the myth about the distinction between the flag of the UK being the Union Jack or the Union Flag. Some people are very keen to tell you that it’s only the Jack when it’s on a ship, and a Flag when it’s on land. This is not true, but it’s widely believed. This blog has a good account of one interview with a genuine vexillologist who patiently debunks the myth, to no avail. But it’s also a good account of the motivations of the people who really, really want the myth to be true.
Towards the end of the programmes, O’Connell put a few listeners’ points to Bartram, including this one:
We need to know the difference between the Union Flag and the Jack because it’s useful to know how knowledgeable someone is to get an idea of whether they know what they’re talking about.
…this is the purest expression I’ve ever seen of pedantry as social ideology: that observance of fiddly little so-called rules is a marker of status.
If you know a “rule” or a “fact” then you can use it to show that you are Right and therefore Better than people who don’t know it and are therefore Wrong and Worse.
The second half of this - why do people do it when they’re objectively wrong - is that being right is hard work. In an ideal world, if we read that e.g. peas are harmful to dogs, we’d all go away and do further research or ask a vet or in some way corroborate this before we went around repeating it. Similarly, the vexilloligist in the interview above had actually gone through the royal proclamations concerning the flag from James VI & I onward and identified that the terms Flag and Jack were used interchangeably with no correlation between land and sea use, and then had traced back the origin of the rule to some Victorians who literally just made it up.
But that’s a lot of work! Some of it quite specialised. We can’t do it for every “fact” or “rule” we come across. Or we could but we’re too lazy. So if you’re the kind of person who likes Being Right then it’s far, far easier to swallow the first authoritative claim you find and latch on to it like a needy limpet and use it as social ammunition henceforward without actually checking.