Flerfs can't understand scale, they can't understand 3d space, they can't understand distances, they can't understand pretty much anything. The world is scary for them, they deserve our pity AND scorn. If only they paid attention in school

They certainly deserve our pity. They’re lonely people who were never great in school and now get to think they’re smarter than others AND have found a community that accepts them.

Unfortunately the very pressures that made them susceptible to the flat earth movement and other conspiracies are the same pressures that keep them from accepting that they’re wrong. “Scorn” probably isn’t a useful tool, even if it feels like the right one (and they absolutely deserve it).

The Socratic method would be far more effective. Continue to ask them questions, accepting as a given that they’re intelligent people and treating them as such. Innocently interrogate them, with genuine interest, about the things they are saying until they reason themselves out of their positions.

But this will only work if they’re someone you know, most likely. Otherwise they’re likely to shun you the first time they come across a question that truly shakes their position.