I heard an interview with Neil deGrasse Tyson recently (sacrilege for an FEr, I know, but in my defense I had good reason). He said in regards to debating flat Earthers and other theorists that he asks the question "What would it take to convince you?"
He asks for what would convince people that they are wrong, then if he can provide that and they reject it, then clearly they aren't ready to be convinced, so arguing with them is pointless. RErs tend to agree with Neil, right?
So I turn the question around on round Earthers. What would it take to convince you that the Earth was flat?
And before anyone asks, it would take proof that there is zero probability (including a sound mathematical proof showing the probability as zero) of a flat Earth to convince me it was round. But if you want to debate that with me, I humbly ask you do so in another thread.