"... artists do not have to be morally admirable people. All that matters is that they create great art. If his own art is to come out of the more contemptible side of himself, so be it."
In both Boyhood and Youth, Coetzee's decision to write in the third person repeatedly proves useful. Imagine the last sentence above in the first person: "If my own art is to come out of the more contemptible side of myself, so be it." Instead of a claim that is both distanced and ironized by the third person, it becomes a pathetic attempt at self-justification, the kind of claim one would expect from someone implicated in fascism, say.
The distance and irony are, as I suggested in my first post on Youth, stronger in this book than in Boyhood. Without ever actually criticizing his twenty-year-old self, JMC manages to make him seem ridiculous over and over again, as happens here with the young man's grandiose claims about himself and his ambition.
But suddenly I see a different way of looking at this. There are two different issues here: being immoral (that is, not "morally admirable") and having a "contemptible side" that one creates with. "John" (that is, Coetzee's self as a young man) has conflated the creation of art from one's darkest impulses with the acting out of those impulses. Surely one can see an artist as creating from "a dark side" while also expecting the artist to not follow through on the impulses that come from that dark side. Artistic works about contemptible acts are one thing (the torture scenes in Waiting for the Barbarians, say); such contemptible acts themselves are another. We do not expect writers to have committed the crimes they write about!
Or to go back to The Master of Petersburg: "... reading is being the arm and being the axe and being the skull." Writing is also a matter of being all those things—but one does not have to have murdered someone with an axe in order to imagine murdering someone with an axe.
In the end, then, the point about art and morality is another comment in JMC's memoirs that one might be tempted to turn into a general statement about his work (that is, JMC commenting on his own work). But such claims in his memoirs are as unstable as markers of how he works as similar claims are in his fiction.