Therefore, the depiction of such magic, taken as fact, is not a positive influence on young, impressionable minds.
It doesn't sound like you know much about kids, either.
I believe that magic does exist, OWK already knows I believe things that cannot be objectively proven so this should come as no surprise to him, and I believe that magic is use of demonic power. What I do not believe, however, is that an author can write into reality a fictional world. Tolkien's Middle-Earth does not exist. Rowling's Hogwart's does not exist. These are sub-creations, below creation (make believe), and as such the creators of these sub-creations can create whatever rules they want for these sub-creations. Just as God created the rule that the area of a circle is always PiR2, and he created the rule that the use of magic is evil, Tolkien and Rowling created their world with the rulesthat magic is neutral and the intent of the magician gives it's use morality. Lewis wrote The Chronicles of Narnia as a work of allegory, and as such he mirrors the real world in his sub-creation, which is why the rules are much closer than Tolkien and Rowling, but this is clearly not what the latter two have done.
As for not knowing kids, do you understand how important using the imagination is for children's development? Up to about the age of 4, most children would have some difficulty distinguishing between real and imaginary. After that time, however, children start having tea parties with their dolls, start playing army men in the dirt, start pretending they can fly like superman, etc. The reading of a book like Harry Potter is easily understood by children to be "make believe".