Depends on what you mean by "rational". My understanding is that many flat-earthers of course don't seriously believe the earth is flat, and the argument is made as a form of artistic expression, which is to say that it is meant to demonstrate that rationality can be abused and does not inherently lead to truth.

One of Asimov's I, Robot stories did a similar thing, with a robot on a space station making rational arguments against the existence of earth.

Of course, there are also nutters...