The civilized people in Twain's Huck Finn don't have any fun, either. They have to do things like sit in church and go to school.
On a more serious note, to be civilized in the novel is to have no conscience. Huck isn't aware of it for most of the novel, but when he befriends Jim he is being uncivilized, according to the home he was raised in and the society he lives in. He is raised by people that actually own slaves, of course.
Huck has a conscience. He thinks that's a negative, but he still follows it most of the time, and rationalizes reasons why he should.
He never directly condemns slavery as a whole, but he does give in to his conscience and, in the end, helps save Jim. This is a very uncivilized thing to do.