If I am not mistaken, they do have a point.   Earth is flat in its own dimension, or 2D.

example: you have a Hubble grade telescope installed in Cape Hatteras, North Carolina @ sea level.  The telescope is facing the east.

Under ideal conditions, you can visualize through the telescope the coastline of the african continent @ sea level and in the same latitude.  Our first reaction would not make us believe this was possible because the African continent is beyond the earth's surface curvature, thus invisible.

I could be wrong though.

I know for a fact that gravity warps spacetime or causes its curvature..