Stephen's Isolation

Through A Portrait of the Artist as a Young Man by James Joyce, the central character, Stephen Daedalus, is an outsider.  However, by the end of the novel it is apparent that this is by choice instead of by any social inability he might possess.  In fact, he seems to see his self-enforced isolation as both a political statement and a prerequisite for becoming an "artist."  He seems to subscribe to the idea that art should be unbiased and therefore feels that he must separate himself from the subject of his art to ensure lack of bias.  For this reason, he rejects his friend Davin's efforts to make him an Irish nationalist.

—I'm an Irish nationalist, first and foremost. But that's you all out. You're a born sneerer, Stevie.—When you make the next rebellion with hurleysticks, said Stephen, and want the indispensable informer, tell me. I can find you a few in this college.
—I can't understand you, said Davin. One time I hear you talk against English literature. Now you talk against the Irish informers. What with your name and your ideas—Are you Irish at all?
—Come with me now to the office of arms and I will show you the tree of my family, said Stephen.
—Then be one of us, said Davin. Why don't you learn Irish? Why did you drop out of the league class after the first lesson?
—You know one reason why, answered Stephen.

Stephen is very critical of the idea of nationalism in this passage, despite the fact that he admits his heritage is Irish. It seems that he is not rejecting his background as much as he is separating himself from the influence of it, which confounds his nationalist friend. A few lines later, Stephen says, "This race and this country and this life produced me[.] I shall express myself as I am." He is not denying the fact that he was born in and molded by Ireland, but at the same time Stephen rejects further outside influence and desires to create his art without any other forces trying to change him.

Stephen's aloofness can also be seen when he refuses to sign MacCann's petition for universal peace.

—I am waiting for your answer, said MacCann briefly.
—The affair doesn't interest me in the least, said Stephen wearily. You know that well. Why do you make a scene about it?
—Good! said MacCann, smacking his lips. You are a reactionary, then?
—Do you think you impress me, Stephen asked, when you flourish your wooden sword?
—Metaphors! said MacCann bluntly. Come to facts.
Stephen blushed and turned aside. MacCann stood his ground and said with hostile humour:
—Minor poets, I suppose, are above such trivial questions as the question of universal peace.

In this scene, Stephen's rejection again seems ridiculous to others.  Why would someone not sign a petition for universal peace?  For Stephen, this is partly because of the imagery associated with the presentation of this petition, but I think mostly because signing would be indicative of the fact that Stephen has a political view.  Stephen's desire to be an artist without bias is so strong that he feels signing such an innocuous petition would show bias.  However, I think that his refusal to sign is also partially motivated by his pride and the opportunity to make a public statement about his self-imposed isolation from any outside influence in his quest to become an artist.