All flat earthers believe, as they must do for their theory to be true, that there is a vast world-wide conspiracy of organizations and individuals that know the earth is flat but that want all of the common people to believe it is round. But flat earthers don't seem to have a coherent explanation of the origin of the conspiracy. NASA is often cited, but the roundness of the earth was common knowledge hundreds of years before NASA came along. For instance, Nicolaus Copernicus published his model of a Sun-centered universe (with earth orbiting the sun) back in the 1500's. In the 1600's, Johannes Kepler did important work involving the mathematics of orbiting celestial bodies. And of course we could name many more famous astronomers from any century.
So the question is, did Copernicus or another early astronomer decide that common people couldn't handle the truth about the earth's shape? Did early scientists decide they could somehow make a lot more money if they lied to the world about the earth's shape? Did the monarchies of Europe have a secret meeting 500 years ago where they made a pact about never revealing the truth? And to this day, the British royal family and all other monarchies have kept the secret, enlisting the help of NASA and the Chinese space agency along the way?
What's your theory, flat earthers?