In April 2003 parodies of Harry Potter were suppressed. Rowling challenged a book about “Tanya Grotter” and won. In July 2005, a Canadian bookstore sold the then new Harry Potter book “by mistake”. JK Rowling, Harry Potter’s author, allowed her publisher’s lawyers to challenge people’s right to read something they had purchased.
Richard Stallman addresses the issue quite well (including further explanation of the Canadian “mistaken” book selling) and he explains further the need for this campaign against buying Harry Potter books.
This isn’t to say one should not read the books, that’s a matter of personal taste and of course one must be free to read. The issue here is about opposing reduction in our freedom to read and opposing reduction in expressive freedom. If you think Harry Potter is worth reading, you can borrow a copy or buy a used copy (no money goes to the publisher when you buy used media).