> Is “flat earth” not in the same camp as “the birds aren’t real”? I.e. never ever accept any possible hint that it’s satire, but it is satire

It probably started that way. But I've met people who seriously believe it. Combination of preferring a force that has its hands on the reins, even if in the shadows, to the anarchic reality human civilisation exists in, and longing for a sense of belonging, with the exercise of actually believing the ridiculous almost serving as a pledge of loyalty.

There is a Netflix documentary on it. They're real, they're having real conventions and everything. They sometimes even try to prove the earth is flat, but fail every time, which somehow does nothing to their convictions.

Unfortunately it is real for some. It ties into the fundamentalist christian sphere, which is a strong ground. I lost a childhood friend over this.

I know people who believe and try to convert others. Also they get aggressive when you find it nonsense. They believe that the govs of the world band together to patrol the ice wall, that education hides the real shape of our world, that all nasa materials are fake and made of deceive us etc. And flat earthers are well known to believe all other conspiracy theories as well and usually fit them in their flat view easily by making up theories that make no sense but spread like wildfire.