It's like a bet. Double or nothing: either you get a supreme place in Heaven^TM for believing the right stuff, or you get burned for all eternity by the all-loving God Satan for asking questions, or believing something wrong, or honestly disbelieving being a horrible, evil person.

If this is true, how can Christians account for logic and reason?

One criticism: you probably should have given Lewis a pass on his criticisms of anti-rationalism. Sure the big-name unbelievers have always been rationalists, but anti-rationalism has been something of a problem among both believers and the less thoughtful unbelievers, and I'm glad to see Lewis combating it. I greatly prefer his attitude to the one promoted by people like Philip Johnson, Rick Warren, and William Lane Craig.

Or have human embryos grow inside things that are not human beings themselves - for example, create a race of non-souled, non-intelligent animals and then miraculously alter them so that they conceive and grow ensouled human beings inside their wombs

Isn't this fairly close to what Catholics believe regarding physical evolution and divine ensoulment?

Why in the world would God even bother to create the Earth if "human birth is important chiefly as the qualification for human death"? Why not just create a race of beings that all die in the womb and have their salvation assured?

There is one possible answer that fits in nicely with the religious zealot's version of the world: People who have been through life on earth have a privileged place in heaven. Probably in proportion to how much you were persecuted during your life. Lewis kind of hints at that:

Apparently He wants some — but only a very few — of the human animals with which He is peopling Heaven to have had the experience of resisting us through an earthly life of sixty or seventy years.

The implication seems to be that those "very few" will be special in some way. It's sort of the extension of the "you'll be blessed more when you're persecuted" way of thinking - you get a merit badge in heaven if you've had to go through the indignity of a physical life. It even fits the idea that Jesus went through that indignity for the same reason.

Driving trucks through the holes in that argument is left as an exercise to the reader.

I can anticipate the apologetic reply here: That a race of beings who all die in the womb wouldn't survive another generation to reproduce.

Ah, but surely an all-powerful god could think of a way around that, couldn't he? Why not have human beings spontaneously generate, the way flies and mice were once thought to? Or have human embryos grow inside things that are not human beings themselves - for example, create a race of non-souled, non-intelligent animals and then miraculously alter them so that they conceive and grow ensouled human beings inside their wombs, all of whom would then die before birth.

Of course, I recognize the absurdity of worlds like this. But these ridiculous scenarios only arise from the primary absurdity that is already posited by Christians, a world where death before birth is far preferable to a full and long life.

Why in the world would God even bother to create the Earth if "human birth is important chiefly as the qualification for human death"? Why not just create a race of beings that all die in the womb and have their salvation assured?

I can anticipate the apologetic reply here: That a race of beings who all die in the womb wouldn't survive another generation to reproduce. Of course, there are still tons of problems with it. For instance, why doesn't God just change the rules? He can make it so birth isn't a prerequisite to get into heaven, and all newly-formed souls go straight there. Alternatively, he could arbitrarily raise the "age of accountability" to 200 or so, so that no one will ever meet it. He is infinitely loving, afterall, so why wouldn't he do this?

Of course, the apologetic response will be something along the lines of "*grumblegrumble* in His infinite wisdom *grumblegrumble*."

There is another typo in the sentence quoted by Alex Weaver: "it it" >> "if it"