Mere Christianity is based on the fallacy of the false dichotomy (well, trichotomy, actually.) It's not a valid justification. It's probably the single worst attempt at Christian apologetics you're likely to encounter, but it's written well enough that you don't notice unless you read it with a critical eye.
You, of course, didn't, because you were already sympathetic to his clap-trap. That's how Christianity persists in otherwise intelligent minds.
You assume I haven’t read it. That’s much like 'bluegenes' assuming that people of faith do not think rationally about their faith. Both are false assumptions. I have read C.S. Lewis and find many of his arguments well reasoned. That is the point. There are rational expositions of faith available.
You may disagree with the conclusion, but that doesn’t diminish the presentation of the content.
You yourself have said that “Mere Christianity” is well written. The process of putting forward a rational argument supported by examples leading to logical conclusions is the process used by Lewis to justify his belief in the existence of God. I view his justification to be rational.
It's not the scientific method, but it is rational
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