I don't think that books should be banned unless they are truly harmful to society and morality in a genuinely threatening manner. By this I mean that books should only be banned if their focus is to openly and plainly advocate and promote such immoral atrocities as racism, genocide, murder, sex offenses, etc......
If people dislike a book to the degree that they feel it should be banned, they should simply dismiss the book and not read it anymore. They shouldn't try and get it banned at the author's expense of not being able to express his ideas and people not being able to read the book.
Both reader and author should have the feedom of speech. Thus, readers should be able to criticize a book (or burn it if they absolutely hate it), but authors should have the security of exemption from banning unless their works are in violation of the above stated.
People can think for themselves and don't need other people banning a book to say that it's bad. People should formulate their own opinion about a book before joining a book-banning-bandwagon. Books should not be banned because a few people got offended or disliked it or took it so literally that they wanted to ban Harry Potter because they believed it was blasphemy to Christianity.