[Cheryl Taggart] moved her hands in groping gestures, half-waving it away, half-trying to grasp it; when she answered, her words did not quite name it, but they were the only words she can find: "You... you're a killer... for the sake of killing..." It was too close to the unnamed; shaking with terror, he swung out blindly and struck her in the face.
Jim Taggart's evil is, of course, on full display here - not only in his disgraceful physical and emotional abuse of his wife, but also in the violence and destructiveness that's central to his philosophy of life. Of course, later he does realize the truth about himself when he realizes - to his horror - that he wanted Dr. Ferris to kill John Galt (even though it would mean his own death).
Is this what he's trying to evade here - the fact that he doesn't want to live, the fact that he claims to want to live while seeking to destroy everything that actually makes life possible? Or is "the unnamed" something else here?