The second is a straw man argument, and given that this is CS Lewis putting words in the mouth of Satan, I read this as the straw man argument.
That sounds to me like you're assuming that Lewis wrote the book so that he could put the devil to say strawmannish things, in order to mock the devil. Which is not the case at all - the demon writing the letters is much more similar to MoR!Quirrel, displaying a degree of rationality-mixed-with-cynicism which it uses to point out ways by which the lives of humans can be made miserable, or by which humans make their own lives miserable. Much of it can be read as a treatise on various biases and cognitive mistakes to avoid, made more compelling by them being explained by someone who wants those mistakes to be exploited for actively harming people.
I read that quote as saying that the Devil (or a demon) deceives people by making them believe those things, not that the Devil believes these things himself. That's how demons behave, they lie to people. This one lies to people about why one should be a materialist and the people fall for it. The point is not to mock the demon, who in the quote is acting as a liar rather than a materialist, but to mock materialists themselves by implying that they are materialists for spurious reasons.
Of course, Lewis has plausible deniability. One can always claim he'...
Another month has passed and here is a new rationality quotes thread. The usual rules are: