A classic tale full of lush language and suspenseful mystery; the story of a young woman haunted by the ever present reminders of her husband's first wife. Clearly this needs to be banned. Though my research has yielded little in explanation as to why Du Maurier's novel is found on the ALA's top 100 Banned or Challenged classics list, I'd like to put forth my theory. As nonsensical as most challenges are, I'm probably completely off the mark. There will be spoilers for those that haven't' read the novel, so tread with caution.
Last fall I took a film and literature class where we studied the novel and Hitchcock's adaptation to film. We discussed much about the fact that according to the movie codes of 1940, ~here come the spoilers~ according to the codes, no killer could go unpunished. in Du Maurier's novel, it is revealed that Max shot his first wife, Rebecca. For the adaptation this had to be changed and her death made accidental. Perhaps some readers also disagreed with the narrator's rejoicing over her husband's murder and his escape from punishment. ~End of spoilers~
Incidentally, in my research I found that Rebecca was the source for codes in World War II, but they were apparently never used due to the belief that security was compromised. Ah, the things you learn on Wikipedia.