There's one major difference I see between the movie and the HP books; nobody in his right mind has ever watched the movie believing that it is meant as a historically correct and morally appropriate representation of the events and more important the movie producers never claimed it to be. JKR in contrast claimed that her books are moral and her parallels to racism and the Nazi Holocaust are realistic.
The movie audience watched 'just another romantic movie about the Titanic desaster'; for many readers of the HP books those were the first and for still a great proportion of the targeted young readers the only series of books they have ever read. This gives the books a much larger influence on the minds of the readers.