But that's just the nature of writing characters; you get out of a frying pan and very often wind up in a fire.

How very true. ;)

I have to say I never saw the Susan problem in terms of sex, probably because in the context of the Narnia books I didn't see Lewis dealing with sex at all. It seems clear enough that he was talking about vanity, and about wilful dismissal of a dear and shared experience with her family, and this seems consistent with Susan's character the way he set it up from the beginning. The only problem I have with the whole thing is that he chose Susan as the demonstration model, rather than, say, Peter (Edmund and Lucy are unlikely choices for other reasons). Is he picking on her because she's female - or just because she's easy? (Easy in the sense of unchallenging, I mean, not sexually available.)

Of course, if he'd used Peter there would probably be much complaining (in a rather different tone) about why a young man's obsession for cricket and fast cars should be so damning. But he didn't use Peter, so we'll never know. This is the problem with fiction; you so seldom get alternate endings.