The book is fiction. Everyone who reads it knows it is fiction. Every fairy tale ever told (I think) relies on magic or talking animals or some sort of necessarily fictitious events. If there is anyone who has read any of the Harry Potter books who believes that they are true, or that they contain authoritative information about witchcraft, it is their own messed-up minds and not the Harry Potter books that is the cause.
(I have read only the first of the series myself— not a big fiction reader.)
Maybe, but true fairy tales, and mythologies before them, have some kind of point, and come from a time when everybody accepted magic as reality (still a few pockets of such, apparently) while Harry Potter is even less magical than Tom Swift.