there are people who think the Earth is flat,
Yup, they have members all over the globe.
There was also this society here in Canada that poked fun of it by using it as their primary proof.
https://search.canbarchives.ca/flat-earth-society-of-canada
Administrative history
The Flat Earth Society of Canada (FES) was organized at Fredericton, New Brunswick, on 8 November 1970 by Leo Ferrari, Raymond Fraser, and Alden Nowlan. They maintained that a prevailing problem of the new technological age was the willingness of people to accept theories "on blind faith and to reject the evidence of their own senses". To promote critical thinking, the society chose to dispute one thing that "scientific Western civilization" considers indisputable -- namely, that the earth is round.
The organization, therefore, set as its primary aims: "to combat the fallacious deification of the circle", "to restore man's confidence in the validity of his own perceptions", and "to spearhead man's escape from his metaphysical and geometrical prison". "The earth is flat; any fool can see that" was adopted as the society's principal motto. Leo Ferrari, a philosophy professor at St. Thomas University, was the society's long-serving president and primary promoter. Other members of the executive included poet-novelist Raymond Fraser, writer Alden Nowlan, writer-educator Alphonsus J. Pittman, and poet-novelist Gwendolyn MacEwen.
To boost membership and advance the cause of planoterrestialism, the executive issued tractates (two by Nowlan), published a newsletter "The Official Chronical" (later an official organ "The Official Organ"), and distributed promotional literature at public lectures and meetings of the Learned Societies of Canada. Ferrari and Nowlan also promoted the society's aims more widely through television, radio, and the public press. They wrote articles, gave newspaper interviews, and appeared on television and radio programmes such as "This Country in the Morning," "Spectroscope," "Take 30," "W5," and "Front Page Challenge".
The publication of William Johnson's article about the FES in Saturday Review of the Sciences (May 1973) resulted in an influx of requests for membership, primarily from the United States. The same year the name of the organization was simplified to The Flat Earth Society to reflect its growing international appeal. Generally planoterrestrialists were drawn from among the well-educated -- computer scientists, university administrators, academics, lawyers, physicians, scientists, poets, and writers. They included such well-known figures as writer Farley Mowatt, television personality Paul Soles, American novelist Lawrence Block, and poet Elizabeth Brewster.
Associate membership was granted to persons "of integrity" who subscribed to the society's aims and submitted an essay giving their reasons for believing the earth was flat. After three years, associate members-in-good-standing were granted full membership status. In 1974, the society could boast approximately 100 members in Canada, the United States, and Europe. Planoterrestrialists waged an intellectual, often humorous, "battle" against the "globularist heresy" for over a decade before fading from view in the mid-1980s.
