Here is Lewis:
"Suppose I think, after doing my accounts, that I have a large balance at the bank. And suppose you want to find out whether this belief of mine is “wishful thinking.” You can never come to any conclusion by examining my psychological condition. Your only chance of finding out is to sit down and work through the sum yourself. When you have checked my figures, then, and then only, will you know whether I have that balance or not. If you find my arithmetic correct, then no amount of vapouring about my psychological condition can be anything but a waste of time. If you find my arithmetic wrong, then it may be relevant to explain psychologically how I came to be so bad at my arithmetic, and the doctrine of the concealed wish will become relevant - but only after you have yourself done the sum and discovered me to be wrong on purely arithmetical grounds. It is the same with all thinking and all systems of thought. If you try to find out which are tainted by speculating about the wishes of the thinkers, you are merely making a fool of yourself. You must find out on purely logical grounds which of them do, in fact, break down as arguments. Afterwards, if you like, go on and discover the psychological causes of the error.
"Bulverism" from God in the Dock
In other words, you must show that a man is wrong before you start explaining why he is wrong. The modern method is to assume without discussion that he is wrong and then distract his attention from this (the only real issue) by busily explaining how he became to be so silly. In the course of the last fifteen years I have found this vice so common that I have had to invent a name for it. I call it “Bulverism.” Some day I am going the write the biography of its imaginary inventor, Ezekiel Bulver, whose destiny was determined at the age of five when he heard his mother say to his father - who had been maintaining that two sides of a triangle were together greater than the third - “Oh, you say that because you are a man.” “At that moment,” E. Bulver assures us, “there flashed across my opening mind the great truth that refutation is no necessary part of argument. Assume your opponent is wrong, and then explain his error, and the world will be at your feet. Attempt to prove that he is wrong or (worse still) try to find out whether he is wrong or right, and the national dynamism of our age will thrust you to the wall.” That is how Bulver became one of the makers of the Twentieth Century."
This is just as prevalent of an argument tactic in the Twenty First Century. For the detractors of Intelligent Design, attempting to explain it away by accussing it's proponents of being Christians, or Jews, or Theists, leaves the argument regarding the merits of ID right where it was, on the side, untouched. Bulverism gets us nowhere, using it as our vehicle of discussion we can gain no ground. Intelligent Design's merits, or lack of merits, can never be discovered by it. The negative reactions I've seen to Expelled, for the most part, are just this sort of argument.