There are some very thoughtless people commenting on this quote (Joe, D.M. and Terry, for example) who have so little breadth and depth of learning that they cannot see the quote in the larger historical context or in the context of Lewis's other writing on society, education, and tyranny; either that or they are motivated in trying to blunt the edge of that which threatens to excise them from the body politic and reveal them for the foreign bodies they are.