In my opinion, bringing up the question of whether or not the New Testament accurately portrays the deeds and words of Jesus is completely irrelevant to the argument. It is obvious that Lewis was using this assumption, and every person that’s tried to use this argument to convert me uses it as well. Challenging an assumption that your debating opponent holds as a basic fundamental part of his/her worldview will not sway things one way or the other.
I think instead we should be examining Lewis’s claim from a logical standpoint:
“If you believe that Jesus was a great man, and that the gospels accurately protray his deeds and words, then you must logically believe that he is God.”
Lewis was directing this argument not at an audience of hardcore athiests who reject Jesus entirely (that would be completely pointless), but at one of atheists, agnostics, deists, Jews, Unitarian Universalists, etc. who believe that Jesus was a great human teacher but not God.
I happen to fall into the latter category–I believe that he was a great guy and had some great ideas, but was, like the rest of us, only human. I was first presented with Lewis’s lord-liar-lunatic argument (it sounds cooler as an alliteration, doesn’t it?) by a born-again Christian student a couple of years ago, and I admit it did take me by surprise and unarmed. After several minutes of deep thought, I came up with an answer, one which I still stand by today:
“Yes, Jesus was delusional. This does not change my opinion that he was a great man.”
In fact, plenty of my heroes are somewhat delusional. Archimedes, as an unarmed old man, was crazy enough to stare down and yell at a heavily armed Roman soldier who had stepped in his geometric diagrams. Galileo was crazy enough to fly right in the face of established “scientific” doctrine. So was Einstein, although he was never imprisoned for it. Ghandi and King were crazy enough to think that they could achieve immense goals without the use of violence. And Joshua Norton, one of the greatest people ever to have lived in the great state of California, believed that he was the Emperor of the United States. (Although I see no reason to disbelieve his claim…)
In short: I feel that I can believe that Jesus was both a great man and a lunatic without reaching the contradiction that Lewis suggested I must.