What societal interest is served by keeping prisoners illiterate? What social benefit is there in ignorance?

Much has been written and much has been said about life in prison. Some write of the glaring incidents of violence that occur, certain that such subjects will grab the attention of the reader. Others play down the violence, lest the reader jettison those dark visions, so distant from his or her experience, as simply beyond belief. As ever, the truth oscillates somewhere in between.