I believe that someone who wants to make a point should have more adept skills at forming and communicating an idea.
As a point of being fair in any argument, it would be best if we took their premise and worded it such that it is communicated clearly. To say that the point is invalid or has no merit based on the skill of the person communicating is avoiding the potential that the argument has worth.
His argument can be distilled to the following:
Has anyone, that believes in the concept or idea that the Earth is flat, and using the zetetic method, actually visited or observed the locations that house the more controversial elements of the concept or idea. This would be via firsthand accounts, with evidence or proof supporting the purported claim, and could be independently verified.
Keep in mind the only difference between the zetetic method and scientific method is the lack of a hypothesis in the former.