Unlike Savage, however, Rossiter is a psychiatrist and is actually serious when he says that. He has written a book, The Liberal Mind: The Psychological Causes of Political Madness, which claims to trace the psychological factors causing people to become liberals.
In a nutshell, the book's thesis is, "My political views are so obviously correct that anyone who doesn't accept them just has to be nuts." It presupposes the truth of a right-wing political outlook and then tries to plumb the reasons why other people do not accept this truth, the conclusion being that they have to be in massive denial. He chastises liberals for being "uncivil, overly sure of their correctness, and willfully ignorant of facts that contradict their worldview."