They used to put them in asylums.
Then came 'park bench therapy'.
Nowadays, group homes are the norm.

Watch the documentary "Behind the curve" about flat earthers. They are the "incels" of science denial and religion seeking acceptance and uniqueness. Just fitting in with the status quo doesn't make them feel special so they have to invent something. That's why religions are constantly fragmenting with schisms. Plus they can now make bucks on social media, write books, get TV coverage, and arrange conferences.

Imagine if a group of nerds rebelled and started a cult that said 1+1 isn't 2 and pi is 4 (like I believe the French briefly did). They'd get laughed out of court, but somehow say the earth is flat or dinosaurs never existed and you get mad followers.

What to do with fools like them?

Make sure they don’t win school board elections.

The only significant difference between intelligence and stupidity is that intelligence has its' limits.