A lot of commentators here criticise the film for not providing evidence that the earth is flat, as if it were created as flat earth propaganda. It isn't. The film focuses on those people who spread the idea that the earth is flat, in a more sociological sense. Attempts are made to explain why reasonably intelligent people might believe something that is patently nonsensical. The point is that there is no proof that the earth is flat, because the earth isn't flat. But people believe it, anyway. Who are these people, what exactly do they believe, and what motivates them? These are the questions the film asks. It has a wider theme of the increasing rejection of science and scientific expertise that Trump has made much more acceptable with large sections of society nowadays, and which social media facilitates. So no, don't expect this film to provide pro flat-earth evidence. There isn't any (the last 5 minutes are hilarious). The film wasn't made to do that.

Flat Earthers seem to be more attracted to belonging to a group of nonconformists than actually proving the world is flat.

My favorite part was near the end when Mark was in his room at the conference talking about the Truman Show. He contrasted Truman, who could escape because by the end he had nothing else to lose, and the town's mayor, who was sort of tied down by the trappings of life. And the director says "Aren't you like the mayor of Flat Earth?" And Mark, who has an answer for everything, was speechless.

Mark actually is trapped in Flat Earth. The notoriety is something he'd never allow himself to give up. If one day he was confronted with irrefutable proof of the planet's curvature, he wouldn't be able to accept it because he cannot walk away from this fame.

Therefore Mark ultimately doesn't want to know the truth. He has no interest in it because his life isn't about that anymore on a fundamental level.

I have mixed feelings about his documentary. On the one hand, it is pretty clear that these folks are being presented as what they are - well meaning but maladjusted individuals who have bought into a down the rabbit hole idea with zero scientific support.

OTOH, it is also unfortunate to give exposure to such utterly bogus ideas. That is probably a disservice to the the rest of humanity.

As for me, I have been an amateur astronomer for over 30 years and can think of at least a half dozen simple tests that prove that the earth is indeed very round. Of course, presenting these to flat earthers would be a wast of time - if they cared about evidence, they would not be what they are.

In the end, the whole idea that such folks with such ideas even exist just made me sad.