The problems with FEs are two-fold:
1) They ask for simple tests that they, at home, can perform to see if Earth is round, but when given such experiments, they put the burden of proof on us and ask us to do it; though we both know that when we come back with results that support the RE theory, they won't believe it.
Either be open for persuasion, or refuse to believe any RE evidence, you can't have it both ways.
2) They offer no evidence to suggest that the Earth is flat, beyond "it looks flat." They offer alternate theories, but I haven't heard a single FE theory that is simpler than it's RE counterpart (such as gravity, sunsets, the horizon), and I haven't heard them come up with anything that seems suspect with the RE theory. I also haven't seen any proof (physical or mathematical) of their theories about universal acceleration, optical illusions, ice walls, or conspiracies. No specifics, like the reason for the conspiracy.
I can understand those here who actually believe in an FE refusing to admit defeat, it is like religion to them... but for those who are simply interested in the academic challenge, it's just annoying and immature for them to leave a discussion once someone presents incontrovertable evidence for RE.