What makes you think the Flat-Earthers are dumb?
It’s been a running joke for decades. They specialize in clever humorous explanations that almost make a sort of sense, kindof like grandpa stories of where babies come from.
On the internet, they’d be called trolls, albeit good-natured ones.
I once heard Alden Nowlan, one of the founders of the Flat Earth Society of Canada, on CBC radio. He was brilliant and hilarious.
Not all flat-earthers seriously believe that the earth is flat. I suspect that most flat-earth societies are really drinking clubs.