At first I thought flat earthers were just a bunch of people on a wind up. Then I realised they are serious, so mentally I put them into the crackpot category I reserve for approx 60% of the people I come across.
Thousands of years ago Aristotle (or was it Erastosthanese (sp)?) proved the earth was a sphere using nothing more than his staff and the length of its shadow at noon as he travelled. Thousands of years later the Internet has given voice to the opinions of those who would lose a game of chess to a bluebottle.
I blame the education system!