jackk > arguing with someone about whether the earth is flat.
Why can’t you argue about that? Repeat the classicial Greek experiment with a shadow angle at different cities. Use the globe or Google Earth. Take them on a round-the-world all-paid trip, let them hold the compass and return to the same place. If people deny the facts would be different. But having unusual opinions is not a crime, it is a plague, a makkah, of our times. How do you know who is or is not a dog on Internet?