On some level, big screen adaptations of beloved novels are always doomed. Hew too closely to the source material, and they’re accused of slavish fan service; diverge too much from the original story, and they risk inciting mobs of obsessives who demand to see S.P.E.W. in all its glory. A successful adaptation must show respect for its root without attempting to translate it literally — something that would be impossible to do anyway, since every reader will necessarily imagine that book’s characters and settings differently.
That, of course, is why book fans often react with violent negativity after an actor is cast in an upcoming adaptation — regardless of who they are and what the role is. And because YA behemoths tend to have younger, more devoted followings than any other genre, the reactions of those followings tend to be particularly hostile.