Flat-Earthers like to employ an extreme, unhealthy “skepticism” toward scientific concepts. We can demonstrate its absurdity by applying the same level of unhealthy “skepticism” toward everyday things that we have taken for granted. We would not be able to know these things and cease to function like normal humans.
It is not hard to “disprove” most of the things we have taken for granted using the same tactic used by flat-Earthers. Keep moving the goalposts and keep pursuing any slight chance, no matter how small, that it might have been wrong.
With this demonstration, most flat-Earthers are actually smart enough to be aware of their reasoning errors. They will refuse to entertain it further out of fear of losing the supposed debate.
Nevertheless, some of these people are lower than a certain threshold of intelligence. They cannot realize their philosophical error and will happily demonstrate it to us.
- Reductio ad absurdum – Wikipedia