It's a joke, that people don't appear to "get". The more upset people get about "Flat Earthers", the funnier it is.
Maybe this was once true, but nowadays I'm afraid the etiology is rather more complicated than that - flat eartherism is now full-on cult territory. I recommend the documentary "Behind the Curve".
Man, it actually sounds like you've fallen for it too, or have I been whooshed?