When Friedrich Nietzsche composed the idea of Der Übermensch, what he proposed was a future where man grew beyond morality, as in theory man could do this if he was sufficiently evolved and morality was originally only a man-made tool invented for practical purposes. There are some who, in their own subtle ways, accept some of these notions, where there are certain extreme conditions that justify different standards for given individuals.
Jerry Siegel and Joe Shuster played with this idea, except they did so with a clear mindset that Der Übermensch was a villain when they translated it to "Superman" and toyed with a comic where an evil psychic genius took over the world. For whatever reason, they turned this idea on its heel, transformed the character's mental abilities into purely physical powers, made the character a hero, and over time made him the complete opposite of Nietzsche's Übermensch, yet significantly keeping the name. In Siegel's mind, he was still tackling the idea of a supreme human, but he came to a radically different interpretation than Nietzsche.
The secret to Superman's greatness is that no matter how powerful he is, no matter how much society changes and no matter how advanced his Kryptonian technology is, he is still bound by eternal and unchanging laws of morality. He is always subject to the law and to ethical obligations ultimately greater than him. The Superman code of conduct has gone strong for seventy-four years as of this writing and has proven its worthiness. The moral to take from him is that if he isn't above morality when he is theoretically evolved to a state of perfection mere mortals can only dream about, then nobody can. He doesn't need them; morals don't serve him, yet ultimately his life holds more meaning when he serves the values he's subjected to.
Meanwhile, Superman's archenemy is fittingly an Übermensch archetype. Lionel and Lex Luthor are, after all, far too sophisticated for the simplistic morals that bind ordinary men. Through the force of their will and determination to find ways to get ahead, they surely demonstrate old conventions obsolete. Standards that bind men like Jonathan Kent are nice, but they're not for Luthors. A Luthor is above the normal concerns of humanity because they are, after all, not normal humans but men who reign supreme in their self-built empire. They deserve that break, and as a sign of their strength they deserve to create their own model for ideal behavior that suites their own vision.
Good for them, except no matter how well they tame their own minds like good Neoplatonists and conquer irrational Freudian psychology based around reproductive instinct, these men and their morality are still subject to reasoning based on basic animal instinct known as the drive for survival. Der Übermensch thinks that he has become like Plato and moved on to that higher realm where the mind departs from matter and the Cave is a thing of the past, and yet no matter what the Luthor's philosophies embrace what is inherently an attribute of survival instinct when they seek self-advancement. Supposedly the prudent man knows to confirm his security, yet he struggles for naught. Just one look as William Cullen Bryant's poem "Thanatopsis" and this point drives itself into certainty. These men struggle against Death, but Death always claims them in the end. How, then, are they being winners by playing a losing gambit?
The common man will never be anything but the common man. He will die somehow or other, and as the ages pass memory of him will fade away as the people who laid him into the ground join him in turn, leaving him no sense of worldly survival whatsoever. Any morality he invents will die with him. There is no empowerment, only false promises. Meanwhile, Superman and his family on the farm held communion with something that never dies, a morality above man. Who wouldn't consider it a privilege to serve such a fine cause? To have that to their names when they pass into that mysterious realm, they can more truthfully say that they lived before they died.