I’ll do you one better, you shouldn’t even spend any time engaging in a debate with people who believe the earth is flat because they don’t want to change their mind.

It doesn’t really matter if the earth is flat or not, for them it’s about being part of a community of people who believe in something that society tells them is wrong. There is no changing minds besides the 1 in a million you hear about and so all the calculations you could do would never work, sadly.