But to put it briefly the agreed term of Rationality is to: Reason consistently within the framework of the goal of a principle or an objective. It's not necessarily logical or truthful in valid terms. Everyone rationalizes really, but the results do not have to be corresponding with reality. Rationality is usually reasoning that is relative to the motivating principle. Which is why loonies can rationalize too. It doesn't unfortunately have the system of fallacies that formal logic has, since it is not agreed upon by a formal consensus. So you can only discredit their reasoning if they are being inconsistent with their idea or principle, but not in the case of being fallacious or lacking valid premises.