Also this situation is not entirely hypothetical, as Astronauts do exist and offer all the evidence and first hand accounts you could ever want.
Cat's exist.
Therefore I am a cat.
Meow meow.
I can post first hand evidence of my catness.
I would say using the argument "It is possible that someone is lying, therefore we should assume anyone who claims a certian experience to have happened to them to be lying" (which is what you summarise there) is pretty much dismissing people automatically. I thought you guys didnt do that?
Sorunx, remember these are not people who believe in a flat earth, they are trolls who like to practice debate skills. Unfortunately, because they have picked a field with a massive amount of evidence against them (the shape of the earth), they have to find a way to dismiss vast chunks of it out of hand, and the way they do this is to claim that everyone in a certain categories are liars, that huge amounts of scientific data have been falsified without anyone noticing and for no reason, even though people using that data in a secondary sense find it works truly for them, and that there is a massive conspiracy that feeds us falsehoods. Even then we find gaps in their claims which causes them to resort to blatant untruths, which when challenged feed back to the "you're a liar" scheme. For example:
Astronaut: "I went to space and saw the earth is a globe"
Flattist: "You are lying and I refuse to accept your first hand account"
Willmire: " I went up in a plane and clearly saw the ice wall and the edge of a flat disc"
Flattist: "Aha! Evidence the earth is flat! I accept it!"
Scientist: "I have performed the Cavendish Experiment and demonstrated gravitational attraction between two bodies"
Flattist: "You have falsified the data."
Rowboatham: "I have done a Bedford Level Experiment showing the earth is flat"
Flattist: "We accept your marvellous true data!"