When might banning books be a good thing?

The ALA (American Library Assn) reports that efforts to ban books these days are primarily aimed at teen fiction that is rife with vampires, sex, drugs and other things that make parents nervous. NY City schools this summer banned The Absolutely True Diary of a Part-Time Indian from reading lists for 11-year-olds. The story is about a 14-year-old Arnold Spirit Jr, with focus on alcohol, poverty and bullying, and it includes references to masturbation and physical arousal.


Most of the bans result from complaints by parents, not from some oppressive government clamp down.So where does the line get drawn? Should there be any lines at all? 


Children's writer Dav Pilkey, author of the Captain Underpants