It's a subtle promotion of a new religion emphasizing magic and ritual and learning
I realize you were making a joke, but even though the Christians who are anti-Potter accuse it of being that, but it's not even remotely a promotion of any religion...much less Wicca. The magic and witchcraft in Potter is standard, stereotypical fictional magic and witchcraft (not remotely Wiccan magic).
Just in case there's anyone around who doesn't understand this yet, let me repeat:
The characters in the Potter series...yes, even the wizards and witches, are culturally Christian.
Not Wiccan, Pagan or any other religion. They celebrate Christmas and Easter...although they seem to do so as cultural holidays rather than as religious holidays (in other words, the same way most of the world really celebrates Christmas and Easter). THere is absolutely no reference to any religious belief or item that is Wiccan.
Magic works for the characters in the book like science works for people. They study it like science (especially Chemistry). It's not religious magic.
Now if we could just explain that to the fundamentalist Christians, we could all take a break.
Actually, those religious leaders who are making the most noise about the Potter series probably do know the difference, and are probably at least aware that there's something wrong with their argument, but as long as it gets them publicity, support and money, they don't care. (Have I meantioned how cynical I am??)
Edited to add: If there are religious values the series promotes, I'd say it was secular humanism, which the fundies don't like either but doesn't get them nearly as much press as witchcraft.