On my news feed today I saw a Newsweek story about how someone found a dvd of Birth of a Nation at Goodwill, not knowing what the plot was.

As far as I can tell the standard for a book being "banned" is just that the librarian or the bookseller is sympathetic to the book's message and thinks it should be more widely read while politicians or parents might think it's inappropriate or they disagree with the message.

If you put the shoe on the other foot and name a book that's out of print because publishers dislike the material or it's problematic in the eyes of librarians, I don't think it fits the standard. Birth of a Nation for example is not a "banned movie" and neither is Song of the South. So the standard is entirely set by teachers, librarians and booksellers.