Their attitude is certainly encomiable, and yet one cannot help but wonder how they could reach such spectacularly wrong conclusions when, in 2023, it is not so

Their attitude is certainly encomiable, and yet one cannot help but wonder how they could reach such spectacularly wrong conclusions when, in 2023, it is not so difficult to verify (in multiple ways) that the Earth is round (thanks to long distance traveling, instant communication, and some geometry). The crux is that human knowledge has progressed so much that "trust your senses" is simply not feasible anymore, as the majority of modern scientific discoveries cannot be verified with the resources available to normal people, and one would need years of study to actually "do their own research" in a productive manner (as I was discussing with the sibling comment, who is convinced that a few days of study are enough to judge neurology research).