Full Idea
There is no such thing as a moral or an immoral book. Books are well written, or badly written. That is all.
Gist of Idea
Books are only well or badly written, not moral or immoral
Source
Oscar Wilde (Preface to 'Dorian Gray' [1891])
Book Reference
Wilde,Oscar: 'The Picture of Dorian Gray' [Penguin 1949], p.5
A Reaction
This is simply false. Novels that are viciously (or subtly) racist, sexist, homophobic, or egotistical can obviously be immoral. I could write a nasty story about Oscar Wilde. It might, though, be very well written. If life is moral, so are novels.