He didn't get banned for saying the earth was not flat, he was banned for calling people morons and idiots. I'm as much opposed to flat earthers as any person here, but calling people with questionable beliefs idiots and morons only serves to make you feel better about yourself. You can explain the ridiculousness of flat earth conspiracy without resorting to insults and you won't get banned as easily.
It’s not like a difference of opinion between supply side and demand side economics.