Noboru has absolutely no sympathy for his mother, and he doesn’t even care if he has lost her respect or affection. Instead, he’s
proud to have humiliated her, because this proves that he has power over her. His claim that Fusako is merely prejudiced against reality suggests that he doesn’t take moral objections to his behavior seriously. Instead, he insists that force and coercion are the true basis of the universe, that he has an inherent right to use them, and that anyone who objects to this right on moral grounds is simply in denial. Of course, in one specific way, he’s right: the only way to stop someone who doesn’t believe in
any moral constraints at all is by overpowering them.