It is as though people need it to be true that someone holding opposing opinions CANNOT possibly also be smart and competent, it's like the ideology possessing his detractors can't conceive of opposition as intelligent. (Notice that this is a phenomenon from left leaning to right leaning, though the right to left version of this phenomenon is something along the lines of: 'this person is smart but ${"evil" | "lacking common sense"}'). I'm fascinated by this.