Some of the reasons people hate on flat earthers
Their whole worldview is based on conspiracies. There's the conspiracy that Antartica is guarded by the military, the ice-wall. Also every air- space- tech related company would be in on these conspiracies too, NASA all the other space agencies around the world, millions of scientists, every
satellite tv cable radio communications phone company, all the astronomers, pilots, sailors any military personnel. They all decided to delete pictures of the ice wall, "firmament" and whatever else would be evidence.
They constantly make up science off the top of their heads that contradicts other science they made up. When you give an explanation for some optical illusion they posted they change the subject, misremember facts, details, obfuscate what you said, outright lie, make up new conspiracies, or the classic "have you been to space?". As if going to space is like going to Six Flags
At worst they are con-men preying on the gullible, at best they are have an OCD like fascination with conspiracies to the point it has become their only accepted reality.