I am trying here to prevent anyone saying the really foolish thing that people often say about Him: 'I'm ready to accept Jesus as a great moral teacher, but I don't accept His claim to be God.' That is one thing we must not say. A man who was merely a man and said the sort of thing Jesus said would not be a great moral teacher. He would either be a lunatic - on a level with the man who says he is a poached egg - or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God: or else a madman or something worse. You can shut Him up for a fool, you can spit at Him and kill him as a demon or you can fall at his feet and call Him Lord and God. But let us not come with any patronizing nonsense about His being a great human teacher. He has not left that open to us. He did not intend to.
We need to distinguish two things, the Trilemma argument as found in Lewis and the Trilemma argument as it might be used outside that context. It's a standard sort of distinction in History of Philosophy disciplines; someone will propose an argument within a given context and someone else will use what is apparently the same argument in a different context, and the two need to be distinguished, because they can sometimes be very different even when word for word. An example: Hume sometimes takes up Malebranche's arguments on causation word for word; but in one case they are given by a seventeenth-century Catholic Cartesian rationalist and in the other by an eighteenth-century Presbyterian-raised skeptical empiricist. They have very different ultimate implications, and would have to be criticized on very different principles, despite the fact that they have apparently identical premises and conclusions. Arguments do not stand alone; they exist as part of an approach or strategy that gives them place and meaning. Malebranche's conclusion, which might be expressed as, "There is no necessary connection between observed causes and observed effects," is intended as an antidote to pagan idolatry and one step in a process of giving God His rightful glory as the Only True Cause. Hume's conclusion, which might be expressed as, "There is no necessary connection between observed causes and observed effects," is part of a theory of belief that is intended to establish the science of man as the foundation of all sciences on purely empirical principles. In a sense, they are about as opposed as conclusions can be, because of the principles that coordinate them with other conclusions. Any arguments and conclusions that move from one context to the other -- like the famous billiard ball argument -- undergo a massive change.
To return to the Trilemma example, note that Lewis has a very particular context in mind. Some people, he says, put forward the following position: 'I'm ready to accept Jesus as a great moral teacher, but I don't accept His claim to be God.' Lewis is responding to this position. The argument is often used by amateurs, however, outside of this context. I think this is not always made clear in the submissions, although one or two touch on it.
But the Symposium is a good example of critique of apologetics within apologetics itself.