Is there an additional step or stage further down the Morlock can descend?
I suggest that there is not. Nihilism is the philosophical belief that no universal truth exists, and thus philosophy as such is in vain. This is the philosophy to which one adheres, knowingly or unknowingly, once one has abandoned truth and reason, embraced the darkening of the intellect by becoming addicted to the self-righteousness of Narcissus, and devoted oneself to sadistic hatred of self-imposed enemies.
Nihilism is a halt-state: once one believes the philosophy that says all philosophy is in vain, one cannot use philosophy to reason oneself out of this position.
If the Morlock cannot change, what happens next?
Next he destroys himself. This is usually done indirectly rather than directly, but notice the enthusiasm which which Morlocks uphold and celebrate everything that is either foreign to them, hostile to them, or mutually exclusive to them. Islamic terrorism is an obvious example, but by no means the only. Even the support of such gentle institutions as schools that discourage learning, art that destroys beauty, and governments that cannot govern has its roots in this self destructive attitude which is the visible sign of nihilism in action.
Morlocks are, as a race, suicidal. They are allured, almost as if under an erotic allure, to images and symbols of death, destruction and decay, to things that are against nature, or that are sterile, vain, futile, and ugly. Go into a modern art museum or watch a gay pride parade to see visible displays of an invisible self loathing.
The flaw is spiritual rather than psychological. While theories about undeveloped amygdala, or the rabbit strategy of welcoming predators into an overpopulated meadow may have some merit, when you see a man who wishes to destroy himself and his homeland, look to the formation of his conscience for the answer to this dark and ugly riddle.
You see a man whose own values, whose own sense of right and wrong, has condemned him to death. Something in his conscience tells him he is unworthy of life.
Now, look next at what he believes, what he tells himself is true.
If he is a hard core Leftist, he believes he was produced by blind natural forces, out of nowhere, and for no reason, blown together by the wind like a sandheap for an hour, to die and blow away again, and never to again live or laugh or love for all the countless eons of eternity.
He thinks he is a meat robot, a thing without free will, without even the dignity of an animal. At least animals are not fools fooling themselves into believing in the illusion of free will. He is the weakest and saddest of beasts.
He also, if he is a hardcore Leftist, he believes that these same blind winds created an injustice so deeply ingrained into society that there is no reasoning with the powers that be, no way of peaceful reformation. Evolution works by the Darwinian law of the jungle, survival of the strong. This is true of social evolution as well (or so his perverse worldview tells him).
If the evils of society cannot be mended by sweet reason, violent overthrow (not merely of part of society, but of the whole rotten structure from top to bottom) is the only alternative.
Hence, for the hardcore Leftist, any love or loyalty to his homeland is a betrayal of his highest sense of goodness and righteousness, because then he is supporting the evils of mankind.
For him, any love of peace or desire for law and order slows the progress of social evolution for the same reason keeping the weak alive to reproduce slows racial evolution.
(Perhaps the Leftist hatred of America keeping the bloodbaths of fascists and communists contained has its roots in this same uneasy sense that violence is needed for progress: by maintaining civilization, the United States during the Cold War and after kept the weak old order alive, and did not allow world war to kill off the unfit so permit the superman to arise. )
Suppose instead of a hardcore leftist, you are merely a flabby moderate leftist.
You have all the same beliefs as the hardcore leftist, but are too weak and silly to call for the violent overthrow of the evil society blind evolution has produced. You lack the integrity to think through your philosophy and come to the harsh but logical conclusions.
You are too sentimental to sacrifice the weak and sick to the great progressive god of Darwin. But sustaining the sick and weak causes racial and social degeneration according to this sick worldview: and so again the conscience of the moderate leftist condemns him for his lack of fidelity. He is a disgrace to the forces of evil.
And so Leftism, the religion that replaced Christianity in Europe since the Great War of 1914, requires a man to believe that he is worthless, less than a beast, less than a dog, but the beneficiary of an evil world-system which must be destroyed, but which he lacks the strength and will to destroy.
Small wonder they want to die. It is a worldview perfectly designed to rob a man of all gratitude and hope, and without gratitude, there is nothing in life but resentment, envy, fear, and disgust.