I don't know where you grew up, but our school library had lots and lots and lots of books that had nothing to do with the curriculum, and students were encouraged to read outside of the required material. The idea that certain books(or indeed, entire categories of books) should be banned from a school library is definitely censorship. It's like suggesting that school computers should be banned from viewing certain pages on wikipedia, on actually, in fact, providing students with copies of paper encyclopedias with pages torn out - it's the removal of knowledge that is the hallmark of censorship.