In this chapter, Helmholtz Watson has been experimenting with poetry that really actually shows true emotions. That's not really what he is supposed to be doing, but he has been feeling unhappy with his work and he wants to write "real" stuff.
So what he does is he writes this poetry about wanting to be alone and how nice it would be to be alone. The students complain at once and he gets in trouble. The reason for this is that you are not supposed to want to be alone. Their whole society is based on always being with other people and having fun. They do not want you off by yourself thinking because that could cause trouble for the society.
So the principal won't publish it because it has "bad" ideas in it -- ones that go against society's needs and values.