as I understand it, the predominant flat earth theory states that there's an ice wall surrounding the edge which is guarded 24/7/365 by NASA-employed gunmen
which is funny because they could easily disprove that by literally going to Antarctica.
In fact, they wouldn't even have to do that, they'd just have to show that a circumnavigation around the edge of the south pole goes in the opposite turning direction as a circumnavigation around the north pole.
Ie. You have to turn
away from the south pole when going "around" the south pole because it's a wall around a disc,
and you have to turn
towards the north pole because you're going around the outside of a circle.