I don't have to prove NASA's existence to you, because you already believe in NASA. As I stated - you are trying to use the fact that we all know NASA exists, to make a completely unrelated point- which is a logical fallacy.
The Earth being flat does not depend on the existence of NASA. She will be flat, regardless of what we humans do.
You fail to distinguish between two things: (1) Scientific evidence of flat vs round earth (2) Explanations about why or how people believe things.
I do not insist on seeing everything before I believe it. I take for granted that Russia exists, for what I think are very compelling reasons. But this is not science.
A physicist _must_ assume most of the laws of physics are true, without testing. But if he/she is in the _field_ of postulating the existence of a new particle, then he/she had better have some direct evidence of that particle that others can verify. Even more for the Zetetic.
As a flat earth believer, I do not require direct evidence of everything in life- just direct, first hand evidence of the Earth's shape.