It seems that flat earthers suffer from an inability to comprehend large numbers. Heck they even suffer from an inability to comprehend the possibility of large numbers.
They can't perceive that the globe of the earth can be so large, that they may not be able to see the curve from their bedroom window.
The other huge hole I see in their arguments is the physical existence of the Earth. There are numerous models which explain how the earth, solar system, galaxy and universe came into being. Why they form into disks, then into planets and so on.
The flat earthers have no such models or theories to explain a flat plane surrounded by an ice wall. They resort to 'we don't know because of the conspiracy' or point you to the Bible.