I hardly think the magic in Harry Potter constitutes Wiccan practices.
In Harry Potter the characters produce magic by waving a wand and uttering latin incantations that will produce a result. The only magic that resembles Wiccan in symbol and in ritual is the dark magic practiced by the antagonists of the story.
Additionally, if you can draw Christian allegory from LOTR, you can certainly draw allegory from Harry Potter. Take for the example at the end of the last book where Harry dies after receiving the killing curse from Voldemort and meets Dumbledore in what appears to be the afterlife. Dumbledore tells him he has a choice - one option is easiest and has him stay here and the other has him return to life and fight the good life and be back in a world of death and sorrow. This is similar to Gandalf who also died and was sent back to return the task that was appointed to him. I'll let you paint any biblical connections to these stories.
Reading stories about magic is not evil, nor does it lead down the path to evil. People lead themselves down the path to evil. The boys who were "influenced by doom" likely would have killed even if they hadn't played that video game. Something else just would have "influenced them". It is up to parents to give children the tools to see what is right and what is right and what is wrong and how to rationalize it in this crazy place.
The world is filled with lewdness, debauchery, sadness, suffering, hate, anger, joy, love, and laughter. Censoring everything is impossible. All parents are accomplishing when they do this is sheltering their child to the point where they can't control them anymore. Some of these kids will have learned on their own how to rationalize the world, but others will be totally unprepared for avoiding excess of the "bad" things in the world. If parents expose their children to vices and other potentially "sinful" things at a young age, while simultaneously rationalizing them, the children, in my opinion, will grow up much better adjusted an prepared to make logical judgements on their own.
By the way, I believe Rowling is a Christian.