Elizabeth Costello objects to Paul West's having thought his way into and brought back to life the executions of people who plotted to kill Hitler. Stephen Mulhall discusses this on pp. 203-213 of The Wounded Animal.
If I were him I would have brought in Plato's story about wanting to go and look at some dead bodies behind a wall (he mentions Plato, but not this story specifically, as I recall). Plato tells the story (as I remember) to defend his belief that in addition to the rational part of the soul and the monster of desire, we also contain another part, one that can get angry when we stoop to such base acts as rubbernecking at faces of death. Costello's view is, roughly, that there are some things we should not look at, some places we should not go. The curious, lustful monster should be kept in some kind of check.
Mulhall contrasts this with an ideal of realism, which demands that we seal ourselves off from no bit of reality. He writes that Coetzee goes ahead and represents the very things that Costello, in Coetzee's story, refuses to represent (see p. 211). But it isn't clear to me that this is true. There is a difference between writing a novel that quotes bits of West's book, on the one hand, and writing a book like West's, on the other. I haven't read all of Coetzee's work, but I don't remember him going into (porno)graphic detail when it comes to torture, rape, and murder.* These things happen, but off-stage. So he does, it seems to me, retain a sense of the obscene. Its existence is not denied, but it is not inhabited either. You might leave one of Coetzee's novels knowing (in some sense, to some extent) what it is like to be, say, him, but not with any improved sense of what it is like to be a torturer or rapist. So here is a point where I think Mulhall goes wrong (although, of course, it might be me that is wrong).
Does Coetzee then fail to be a true realist? Well, perhaps that isn't what he really wants to be. But no, I don't think he does fail in this way. Preserving the phenomena, capturing the facts, keeping it real means not pretending that obscene things don't happen, but also not pretending that they are not obscene.
*I'm not saying that West does this, but it seems to be Costello's view that he does.