I do not know the shape, size, dimensions of this place we call Earth. You'd be wiser to admitting the same thing. I do, however, know how water behaves - it always displays a flat surface despite what is underneath it, it can't bend, it can't display convexity of a shape on the surface. This is the experience of every single person alive or indeed everyone whom has ever lived. This common knowledge of how water behaves denies a globular earth. Of course you are freely open to challenge but you must display evidence of said claim. The claim of a globe Earth deny this practical reality.

Surely if we are to try and engage in a reasonable discourse then we must agree to first principles.

Idealism over realism? Fuck that.