[These posts always get so much longer than I anticipate...]
TPA- the ministry also seems to have overlooked the awful potential of polyjuice potion.
D&D, and now Harry Potter, are not considered on the same level as Black Masses, but more as gateways to the occult. Much as cigarettes and pot are considered gateways to harder drugs. The problem (and different people have different levels of problems with HP) is that Rowling has used a small (VERY SMALL) amount of real occult material in her books. Reading the tea leaves, gazing into crystal balls, alchemy, etc. Personally I believe both have been tarred unnecessarily, and tar's a pretty sticky material; difficult to remove once it gets onto the skin. D&D problems were started because one kid got crazy about it and killed someone, and because that particular kid was into satanism, the rest of the phenomenon became associated with it. And problems with Potter, I'm told, stem back to an article written by The Onion, in which a child gains an interest in the occult as a result of reading Harry Potter. Obviously the overly literal and zealous person who read the article didn't understand what The Onion was.
Do Christians believe in magic? The answer is that some do, some don't. Some don't believe in any of it, and that warnings against it in the Bible are for the purpose of keeping people from being deceived into trusting in things that don't exist. Others believe that all things magical, that have every appearance of being true (this often includes "miracles" by members of other religions and other paranormal activity, conversations with the dead, etc.) is accountable to either demons or to Satan himself. Most evangelicals fall into this category. And there's a third group that actually believes in all things magical, but they are definitely a small minority. And you'll find all three of these types coexisting in nearly every church, and even mixtures of the three in the same person.
I don't buy into the "it's just fiction" argument, because that would be to render the written word impotent, and if it's inherently impotent, why's it the first right guaranteed to us in the Constitution? Clearly words have power, and thoughts have power. This extends into fiction, not because people literally believe in magic or the fantastical, but because authors can't help but write their worldview into the books. And some worldviews are harmful. I don't think Rowling falls into this category and have argued against her inclusion in it. Nor is it automatically wrong to read the views of someone that disagrees with you (and it's healthy to get a certain amount of disagreement); but it does mean you need to read attentively.
And then there's the Narnia/Tolkien case. Both books explicitly use the word "magic", yet very seldom does any Christian seriously object to it; largely I think because both Lewis and Tolkien were avowed Christians, so clearly they weren't using the word in the same way as a non-Christian might. It's rather ludicrous to object to Potter while not objecting to Narnia, and this gets into the reasons
why magic is condemned in the Bible. The occult's goals are generally: to curse someone (as in voodoo), to talk to the dead (as in channeling and seances), and to see into the future (fortune-telling, tarot, and quija boards). If the power to do this (since people who practice it claim it really happens) is real and it clearly doesn't come from God, then it must come from the devil. So you have a reaching by humans for a power that not only isn't God's, but is the devil's.
Within the context of a fabricated world, however, all of this changes. The power isn't necessarily attributed to Satan or to God; the power comes from wherever the author decides it comes from. It isn't, therefore, inherently evil. The power itself becomes neutral, much as mankind's seeking control of the natural world is neutral; it's good or evil depending on the use to which we put it.
Nor is it put to the uses it's put to in the real world; no occultist believes they can fetch their sugar bowl from the cupboard and command it to teleport up the stairs on its own, or turn their cat into a dragon. There's still room in a fictional world, however, to attribute things to devils and to "evil", so if the author attributes his/her magic to dark powers, then it's still a problem for Christians.
Please remember that
rabidly anti-Potter people are a minority within the church (mildly anti-Potter people are much more common), and the internet has a tendency to bring out the kooks from all corners of human opinion.
edit: JD- no, they don't know what the word "occult" actually means. It's come to carry such a strong connotation of satanism that that is the working definition within churches, rather than the more proper meaning of "concealed" (or mysterious). This problem traces back to the day when science and alchemy weren't separate; and demonstrable results of alchemy (scientific results, but since there was no science, it was considered magic) were attached to the occult, and as this happened about the same time as the Puritans were running about on witch hunts, and moving to America (and in the process, semi-disconnecting themselves from the context of the culture they came out of), the whole thing's just gotten to be a big mess.
edit (again): and it's not like Christians only sit around and discuss the evils of Harry Potter. It's only one issue among very many, but being as it's one of the few places where fantasy and Christianity intersect, it appears to be larger than it is.