A form of censorship, protest, or hate mongering.
"A library's mission is to facilitate the spread of information. There is no greater action contrary to this goal than book burning. Since ancient times, people from virtually all religions and societies have burned books as a form of censorship, protest, or hate mongering."
University of Wisconsin-Milwaukee Libraries have created an interesting web-exhibition on "Book Burning through the ages" with some selected titles featured and a list of primary source links for further research. Great for promoting discussion with students.