Well, Columbus, Galilei, Kepler & co. challenged what was considered “established fact” about the shape and place of the earth in their times.
It is not wrong to challenge what is considered “established facts”. Problem is when you discard results that are going against your preoposition. I wouldn’t consider flat earthers to be particular religious as a crowd though. At least in my country they mostl come from the esoteric scene, where you get a mixed bowl of esoteric nonsene, conspiracy theories, and fascist ideology.