The way I view it, it's more likely to expose fundamentalist Christian kids to fantasy books than anything else. I don't really think that there's a reason Christianity can't be a basis for a fantasy book any more than Graecoromanishm, except that random fantasy readers don't like Chirsitianity. I've read good fantasy books that have much worse deus ex machinas based on nothing in particular. Also, Narnia is much more openminded about several things than most fundamentalist Christion thingies. Sometimes I think people aren't willing to pay the price of openmindedness: it's a two-edged sword.

(Note: this opinion is from the perspective of someone with little exposure to Christianity or any particular Bible who had a strong positive influence in his childhood/life from the Narnia books and a short negative influence when he encountered Christian interpretations of them by chance on the Internet much later. And who read the whole article. And who animals/trees having souls affects more than your average reader. And who should go to bed soon.)