I wonder then if the decision to read fantasy stories ought to be left to the individual. This is along the lines found in Romans 14 where Paul writes that each individual is responsible for what they take in, but they ought to take care not to cause a brother to stumble.
I think there are degrees of influence, degrees of error that need to be considered. When I read a book written by a Christian, I have to filter some stuff out as non-Biblical, merely opinion, irrelevant, or misinterpretation, or worldly influence.
====
With Lewis' Narnia and Space Trilogy, there are a
few areas that should be filtered out as unfortunate decisions on Lewis' part, as a Christian author. On the positive side, Lewis does do some theological exploration on the subject of why magic is evil, and how miracles or the actions of naturally gifted beings with secret knowledge approved by God may operate. In The Magician's Nephew, the magician is clearly presented as an evil man -- he manipulates formula to utilize secret knowledge, it is forbidden, he is not guided by God to do it, his motives are bad, his character is evil. The witch he meets, by way of comparison, is demonic, she is not a child of Eve, she naturally has various magical powers and finds the magician's technical manipulations to be inferior. Both are clearly shown to be evil characters who ought not be emulated. On the other hand, in Dawn Treader there is a being on an island who is actually a star, a spiritual being of some kind, who has a book containing formulae; various creatures have natural abilities that are magical but they aren't evil, and they aren't human. In the instance of the star, one of the girls is tempted to use one of the formulae against Aslan's warnings -- she almost falls. Unfortunately, centaurs do astrology, but they are not human, they are not on earth, and they may simply be able to communicate with star beings, it isn't presented as ordinary astrology, they somehow discern what the stars are saying; I wish it was presented better theologically, or avoided. Also unfortunately, there is a wise-man advisor to Caspian who may engage in forbidden arts, and I don't see any theological dealing with the subject, any presentation of concerns about his activities; but he isn't exactly a wizard, it's hard to say just how much of a wizard or occultist he may be; I wish it was clearer for the sake of not encouraging what is forbidden, but on the other hand, it isn't a clear encouragement of anything forbidden, I don't think. And in these cases, these are not major characters, the advisor is not set up as a major hero, and the centaurs, not being humans, may simply be able to communicate with such beings as the star on the island. Also in Space Trilogy there is communication with angels who preside over planets that I wish was handled just a little bit differently, to distance the worldview and speculation more away from certain hermetic and medieval speculations, to reduce the possibility of rationalizing or encouraging such things. In Space Trilogy Merlin, who was frozen asleep, is brought out of sleep and is used to take down an evil organization with the help of these angels from the planets, but on the positive side, he is sternly rebuked for dabbling in forbidden techniques and abilities; Merlin is called to repent and sanctify his ability to be guided by spiritual beings and act with various powers, by submitting himself to God's limits. In these handful of unfortunate cases where one may possibly be lead to rationalize or glorify dubious or forbidden explorations, there is also on the positive side, theological exploration and speculation about how and why various acts are immoral or forbidden, for spiritual beings or mankind or for other beings God might create, and concern for acting according to God's direction, obediently.
Lewis briefly incluse mention of various mythological beings and gods in Narnia. He clearly represents them as mere creatures with natural abilities and functions according to God's direction. Lewis in a few instances is very near the line of orthodox speculation. He could have refrained, and it would have strengthened his books, made them more suitable for Christian enjoyment. He includes a character who gazes into a lake to see visions, refering to this as an art. He isn't a major hero, but as a minor character he plays a positive role, and this along with the Centaurs who read the stars, are among the few major gaffes by Lewis. Lewis's work would have been better if he played a little more cautious, deciding to hover less near that boundary of orthodox speculation, to reign in a bit. That said, when he wanders near that line, he does present theological food for thought about the line, and often raises the theological issues into awareness.
So Lewis' issues are similar to the issues found in conventional folk-tales. Sometimes speculation about the lives of various beings gets to be dubious. But on the other hand, like conventional folk-tales, witches and sorcerers are presented as evil characters, though various unusual beings have powers and people sometimes dabble with the forbidden and come through by the skin of their teeth.
======
Both Lewis and conventional folk-tales are sometimes too casual about forbidden speculation and forbidden practices. Handled with care and filtering, a Christian may benefit from some of the stories. Lewis is far more cautious than many conventional folk-tales when dealing with such issues. Lewis' fiction is far more edifying for a Christian than Grimm Fairytales. Like Beowulf and Spencer's The Faerie Queen, there is caution against magic and enchantment, fighting against evil beings, and encouragement of virtues, and Christian references, but unlike these works there is more specifically Christian theological speculation going on.
======
Tolkein features Gandalf as a major character. On the positive side, Gandalf is actually an angel of sorts who comes to earth, in Tolkein's world, and just about all humans who crave, seek, or use magical incantations/power are shown to be warped by it, not to be emulated. Unfortunately, elves and dwarves and these angel-like beings like Gandalf do use incantations and secret arts to harness natural powers, and this does glamorize such things as using magical crystals or magical runes. A serious problem for Tolkein is the Silmarilion, which features a gnostic-like creation account, where various angel-like beings (of a higher order than Gandalf) are in charge of various aspects of creation, much like that found in pagan myth, and like gnostic speculation, the evil angel-like being who falls has creative powers. Tolkein crosses a line that Lewis does not. Lewis hovers the line of orthodoxy in his speculative fiction, which is problematic but not a fatal flaw. Tolkein crosses the line and in the Silmarillion he presents rank heresy as entertainment. The Lord of the Rings itself doesn't go into the details of the back-story of the Silmarillion, at least. Tolkien doesn't use such speculations and alternate world situations to explore theological questions, and when there are theological aspects to his speculation, it is reminiscent of heretical qabalistic/hermetic/gnostic speculation, involving a worldview where many created beings do the creation work for God. If it weren't for the Silmarillion and the heretical quazi-qabalistic/gnostic speculations involved in the background creation story and history of Middle Earth that lies behind The Lord of the Rings, it would be more like Beowulf and Faerie Queen.
=====
With Potter and Twilight, magic, blood-drinking, etc., is sensationalized, the enchanters who do incantations or vampires or werewolves are
major heroes, and these subjects are
pervasive. This makes a serious difference to me. Why do I want to watch something where the 'heroes' are involved with such evil? The main human (or once human) characters and heroes do magic, they use incantations, they talk to the dead, they use runes, etc. The author of Potter admits that 1/3 of the magical material traces to real historical and folk material on magic. And it is presented as positive. It IS the story, it IS the heroes. Glamorization of magic powers and techniques and learning, all through. Forbidden studies are 'good' in this 'alternative world'... VERY difficult to filter out all that is wrong with this. Our hearts urge us to agree with what we find entertaining, to approve, to laugh, to treat it casually, to endorse it, to excuse it. No such constraints as those found in Lewis or Tolkein. And as far as unorthodox speculation goes, Potter and Twilight not only present decidedly non-orthodox spiritual worlds (a problem with Tolkein's Silmarillion, where evil angel-like beings are said to have creative powers, and there are various angel-like beings which are co-creators), Potter and Twilight are re-visionist about what is good or evil: they decidedly take the stand of denying that that which is evil is evil, no, they do more, they call that which is evil to be good.
However, why must the mentality be that Christians who chose to read Harry Potter and LOTR for their stories aren't following Christ? I don't think our salvation is dependent on what we read or do not read.
As a heart-issue, we should want to steer ourselves more into what God loves/approves of, and away from what God hates/disaproves of. Lewis' Space Trilogy and Narnia could be improved in a few areas, filtered in a few areas, and be quite positive fantasy speculation. Tolkein and traditional fairy-tales require a bit more filtering, but at least in the best stories the main heroes are trying to be freed from evil wizards and witches, and magic is presented as dangerous for people to dabble in, something forbidden that evil enemies use.
Harry Potter -- why encourage the heart to enjoy such things, that is the challenge I'm putting out there. The other fantasy materials one should be careful with and filter, and yet the best of them don't encourage humans to seek to become a wizard but rather warn of the danger, don't present vampires or werewolves as beings to sympathize with or to emulate, don't encourage conversations with ghosts.