Have you ever seen an asteroid in person?
I have never been to space but I've seen LOTS of asteroids that have hit the Earth's atmosphere, and lots more that have landed on the surface of Earth. I've even touched some! Are we only allowed to believe in things we have personally proven to ourselves?
The overlap and association between flat earthers with Christian literalists is interesting to me, because flat earthers refuse to believe anything they can't see for themselves and Christians ONLY believe things they can't see for themselves, and yet one of these groups gave rise to the other.
You can literally measure isotope abundances yourself at your local university. You can take intro physics and then minerology and work up the concordia diagram all by yourself, and you can, independently and without any prior suppositions, prove to yourself that a particular rock is billions of years old. No belief required! The flat earthers should love it!
In the exact same way, you can measure the gravitational constant of the universe with lead weights, or the speed of light with a rotating mirror, or the exact value of pi by dropping needles on a tiled floor, or the circumference of the earth with an hourglass. These are historical experiments that real people really did, and you can absolutely reproduce them yourself.
How is it that modern humans take the totally opaque miracle of the internet totally for granted like it's no big deal, but absolutely refuse to believe in science they can reproduce at home? I'm baffled.
Well, okay I'm not that baffled. As several people here have already pointed out, there is a very strong contrarian conspiracy theorist streak in the current zeitgeist. I'm sure there's a huge amount of overlap between people who believe the Earth is flat and people who believe the deep state is using fake news to discredit the most honest President ever. It's only a matter of time before DJ Trumpenstein weighs in on the flat earth debate (via Twitter, of course). I'm guessing he'll say there are "some very fine people on both sides" of this issue.