In 1992, Father John Murphy tutored me for the AP English Literature test because I wanted to take Shakespeare from Matt Barmore and Mythology from Bob Grady, and I didn't also have time for AP English. In addition to the standard Paradise Lost, Father Murphy and I also discussed John Milton's Areopagitica. As the president of the Debate team, he knew that I would be interested in the freedom of expression outlined in that speech, and summarized in in the line:
"Give me the liberty to know, to utter, and to argue freely according to conscience, above all liberties."
I mention this because September 27 - October 4, 2008, is designated Banned Books Week by those who are concerned by such issues. (A quick look-up shows that Milton's Paradise Lost appeared in the 1732 Papal Index Librorum Prohibitorum, as seen below.)

Index librorum prohibitorum ... Gregorii xvi ... jussu editus. [With] Appendix [1]-4 By Index librorum prohibitorum
According to the American Library Association, over 400 books were challenged in 2007. To see the list of most-challenged books, visit the ALA's website. I was surprised to see that on the list of the year's most-challenged authors, Mark Twain is still #3.
I make note of Banned Books Week in hopes that we take to heart the oft-quoted ideal of the Jesuits to be counter-cultural. One of the most important skills that we can teach our students is to think critically. To do so requires exposure to materials that are thought-provoking, the ability to reason, and the liberty to communicate.
Long before there was talk of any 21st Century Skills, Oscar Wilde was on to something in the preface to The Picture of Dorian Gray: "There is no such thing as a moral or an immoral book. Books are well written, or badly written." Our job is to give students the skills to know and communicate the difference.