Flat earth belief falls into the same 'this is stupid' category as: 
* holocaust denial 
* climate change denial 
* denial that the 'alt-right' really isn't about white supremacy and nazism 
* the birther movement 
* the believe that Trump's inaugural was bigger than Obama's 
* Trump's believe that the Russians didn't interfere in the elections in almost half our states, but that millions of people voted illegally, all as Democrats 
* believing that the Republicans "better" health plan is really better (but if you count tens of millions of people losing their health insurance and tax cuts for the rich as being "better" then I suppose it is.)