I never argue with flat earthers.It might push them over the edge.
Never appeal to a man’s ‘better nature’. He may not have one. Invoking his self-interest gives you more leverage. Robert Heinlein, American Science Fiction Author.
When you think about how huge the Earth is, and how the Earth is just a tiny ball orbiting the sun, which in turn is a minuscule speck in the universe... It's pretty easy to rationalise eating an entire tub of ice cream all by yourself.