aquadoc, I agree more than you know, this "idea" is so dumb it truly numbs my brain trying to fathom the depths of stupidity this springs from.
The primary issue, though, is not the earth being flat, or the universe revolving around the earth, if lizard men rule the world or any whatever the subject of their conspiracy is. Its that there is a conspiracy, any conspiracy. These people need the conspiracy. Most of these people are not what you would call a success in any facet of life, but they see in themselves fountains of brilliance and potential. Why aren't they at the top of the heap? They have to believe there is a conspiracy to explain why they are so unremarkable, why they are failures, why no one recognizes them. If the conspiracy is so large and has been pulled off for so long, and that almost the whole world is convinced, then it also powerful enough to stifle the greatness down to each individual person, the greatness they know is in them. It's not their fault they are screw ups, its the conspiracy; the man, men or lizards behind the curtain pulling their strings too. At the same time, the fact that they are aware of the conspiracy while everyone else is fooled, gives them a sense of superiority. Evidence to the contrary, even in overwhelming amounts, merely reinforces the extent of the ruse, and inflates their opinion of their own "knowledge." Nor do they want to prove their beliefs. Do they ever attempt to see the ice walls that surround the seas that NASA has snipers on top of? Of course not. To do so would shatter their own shield.
Even if you were to shatter the flat earth conspiracy ,voila, like a Matryoshka doll there would be another conspiracy to take the place. Maybe it's just Communists in Congress or the fact that the New World Order runs America via mind control drugs secreted in Kentucky Fried Chicken, there will always be another. There can not, not be a conspiracy. No conspiracy lays bare the fact that their failure is theirs alone. Given the choice between a conspiracy and admission of their own inadequacy, they'll go moon bat every time. They need it like a junkie needs the needle.
Realize, I'm not trying to argue with you. I'm trying, in my own mind, to get to the point where this can argued in the appropriate manner, and the root issues have me baffled as to how to tackle it. It's not evidence, we know the earth isn't flat. It's who the people are inside who believe the lie. Oh...and I'm not a psychologist, I only played doctor in college