By making your prototypical example of a dubious minority opinion the flat Earth theory, I think you risk falling into bad mental habits. If you go round thinking "people who disagree with me on subject X are just like flat Earthers" then you're doing both them and yourself a disservice -- yourself because no matter who you are it's certain that on some issues it's you who are wrong.
What I'm saying is that flat Earth is a bad example because it maps poorly onto just about any other real-world disagreement.