At least these people understand their audience's intellectual limitations.
For the record, I circumnavigated the world solo in a 31-foot boat (https://arachnoid.com/sailbook/). From direct empirical evidence, I know the earth is round.
Of course, I believe you! I'm not a flat earther. But to someone who has already made the mistakes necessary to convince themselves that the earth is flat, it's easy to deny your proof. You don't have direct empirical evidence, you have the evidence that you went in a loop, plus a bunch of science that these people have crazy reasons for denying, and that science tells you that loop involved going around a sphere.
Antartica is not an island continent, but an ice-wall that extends around the entire flat earth
Nobody has ever got a photograph of the edge because you can't go there, you're not allowed. The governments of the world see to that!
It's all delightfully solipsistic...
Yes, plausible explanation, which partly explains how beliefs like this can persist. Ironically, an increase in mathematical and geometric sophistication can produce more convincing alternative models -- for those who want to defend the alternatives.
Not if one's satellite navigation system fails and one is then required to reduce sextant sights to get across the ocean safely, as happened to me. I had a laptop on board and wrote a program to reduce my cheap plastic "backup" sextant's sights in a reliable and speedy way. I ended up with almost the same position accuracy from the sextant that I was getting from the failed satellite navigation system (this preceded the GPS era -- GPS is way more accurate).
So from my perspective, being a software person was a distinct advantage, and I assisted a number of other sailors whose non-cybernetic navigation methods would otherwise have gotten them into serious trouble.