Not being into black magic myself I'll take your word for it. Hmmm, you seem to know a lot about it...
All kidding aside, let's look at my "strawman": you are clearly drawing a cause-and-effect relationship between Harry Potter and real life black magic. "Any similarity to real life witchcraft is surely coincidental" (no sarcasm tag but I could hear it all the same.) Given that millions of people, children and adults alike, have read the books and seen the movie we should see a huge upsurge of self-mutilation, shouldn't we?
My concern is that children are being exposed/desensitized to obscene violence and horrific occult practices.