The banning of books is against our United States constitution because of how it contradicts our freedom of speech. We have the right to say what we want even if it goes against someone's beleifs. To ban a book is to ban a voice.
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."