The Greek astronomer and mathematician Eratosthenes worked out the Earth was a sphere in the 3rd Century BC, so it's not like the Earth being a big blue ball in space is new. Even so the belief the Earth is flat, or some other non-spherical shape, keeps resurfacing throughout history like a particularly illogical rubber duck.
The idea has attained a weird level of fashion today, with NBA players seeming particularly prone to either actually believing the Earth is flat, or using the idea to troll reporters for some classic locker-room stories later.
A related idea is that the Earth is hollow, with a hole somewhere allowing a special group of enlightened souls to enter it. This hole used to be in Antarctica until the whole globe was photographed and showed it wasn't. All sorts of exciting nonsense was posited to exist on the inside, from dinosaurs to Aryans (this one was big among the proto-Nazis of the early 20th century) or a limitless source of magic energy.
The conspiracy element of the non-globe theory accused the world's governments, scientists and educators, and especially NASA, of fabricating evidence of a spherical world. Quite why any of these people would go to the trouble and expense of all this is less easily explained.
Ben Counter is a fantasy and science fiction writer, gaming enthusiast, wrestling fan and miniature painting guru. He was raised on Warhammer, Star Wars and 1980s cartoons that, in retrospect, were't that good. Whoever you are, he is nerdier than you.