Mond is rejecting a book that was written by an Alpha worker. The book is too profound and could potentially threaten the state. The writer will therefore be sent to an island, far from civilization.
The US Marxists Bowles and Gintis argued that schools help to maintain class structure and social inequality by discouraging independent thinking. They found that creative and independent students often prefer to do things their own way, not listening to the teacher at all. This threatens the teaching, moral lessons and carefully maintained status quo of the school, and of society in general. Schools wish to encourage pupils to conform to society rather than question it. For the same reasons, Mond needs to discourage independent thinking that questions the state. Find out more about Bowles and Gintis' theory here.
Throughout history, many different governments, societies and institutions have banned books, as Mond decides to do here. This form of censorship usually has political, religious or moral motivations. Many well-known or important books have been banned by various societies, including Alice in Wonderland, Animal Farm, The Canterbury Tales, The Da Vinci Code, The Diary of Anne Frank, Lady Chatterley's Lover, Nineteen Eighty-Four, Ulysses and many more. Brave New World itself has been banned at various times for its descriptions of sexual promiscuity!