Technically, this isn’t even a case of religion going crazy. The flat Earth conspiracy actually started out in the German Nazi party and were eventually pushed out because even the Nazis thought they were too crazy.

Notice how many of them mention a vague “they” as the ones maintaining the conspiracy. That’s them referring to Jewish people. While this is notmal for most conspiracy theories, few directly originated from the Nazis.

If you want more detail, there’s a couple episodes of Behind the Bastards explaining it. I recommend giving them a listen