The primary issue with Rothbard's “Egalitarianism as a Revolt Against Nature” is that the primary argument rests on a Straw Man fallacy. To wit: “This means, of course, that equality of all men—the egalitarian ideal—can only be achieved if all men are precisely uniform, precisely identical with respect to all of their attributes. The egalitarian world would necessarily be a world of horror fiction—a world of faceless and identical creatures, devoid of all individuality, variety, or special creativity.” The substance of his argument -that the philosophy of egalitarianism, when taken to its logical conclusion, is morally abhorrent- is, in fact, quite valid. However, Rothbard's reasoning, resting as it does on an inherently fallacious mechanism, requires further expounding in order to be considered a defensible theory.
Primarily, a greater understanding of egalitarianism is required. This philosophy, when carried out, is nearly indistinguishable from hardline communism. Greater equality is seldom intended to mean building the masses up. It is, rather, as C.S. Lewis put it, “democracy in the diabolical sense”: bringing society down to a level that most people are capable of, and not permitting anyone save the rulers to rise above the general limit. This may not -technically- be what egalitarian philosophy professes to desire, but all theories must be viewed in light of the real world, rather than the world of theory. And in the real world, egalitarianism has never been used as a tool for anything save “democracy” in the sense of “you have no right to be better than me”. Indeed, egalitarian movements have historically been dedicated to drumming up support by promising to plunder the wealthy, then proceeding to tear down the edifices of society and proclaim paradise in the rubble. Witness the Soviet revolution, which exterminated the Czar and the upper class of Russia, along with anyone suspected of supporting them. Far from leading to paradise on Earth, this led to mass shortages, famines, and economic devastation.
Furthermore, egalitarianism is morally abhorrent in the lights of Kantianism, Natural Law theory, Utilitarianism, and Virtue Ethics alike. Rothbard has already detailed at length the shortcomings of egalitarian philosophy when compared to Natural Law theory, so I feel little need to launch into any further examination. “The intuitive recognition that men are not uniform, that the species, mankind, is uniquely characterized by a high degree of variety, diversity, differentiation; in short, inequality. An egalitarian society can only hope to achieve its goals by totalitarian methods of coercion; and, even here, we all believe and hope the human spirit of individual man will rise up and thwart any such attempts to achieve an ant-heap world... we recognize that such a world and such attempts are profoundly antihuman; being antihuman in the deepest sense, the egalitarian goal is, therefore, evil and any attempts in the direction of such a goal must be considered evil as well.”
Utilitarianism, in fact, would be the theory one would suspect of having the most in common with egalitarianism. However, even though there is no higher measure of morality than the greatest pleasure for the greatest number under this theory, egalitarianism is inherently antithetical to the philosophy of Utilitarianism. The means by which Man has raised himself from tribal hunter-gatherer societies to the modern industrial age is innovation. Egalitarianism would stifle this innovation that has brought so many benefits to humanity. Rather than plundering the able in order to sustain a brief period of orgiastic delight, it is in the best interests of Mankind to build up innovators so that the rest of society may enjoy the fruits of their labors.
Virtue Ethics and Kantianism, with their emphasis on treating humans as beings with inherent dignity, must of necessity react to egalitarianism with repulsion. It is abhorrent to reward those who have made something of themselves by looting all that they have created in a vainglorious and vain aggrandizement of some redistributionist ideal. Utopia does not, in fact, justify the means, all the more so when this utopia will never be achieved and attempting to do so will lead to nothing but suffering in the short term and ruin in the long term.
Finally, egalitarianism is futile in the economic sense. As I stated in my brief reflection on Utilitarianism above, the celebration of innovation and risk-taking has raised Man to the state he currently enjoys. To act as the ancient Greek despot did and cut down anyone who rises above the general mass is to commit economic suicide. Punish those who attempt to create and raise themselves above the rest, and you get stagnation at best. At worst, you get ruin and collapse. Witness the ruin of every redistributionist state ever attempted. The indolent decline to make any particular exertion, knowing full well that they are protected from the consequences of their laziness and stupidity. Meanwhile, the industrious have little motivation to work any harder than the rest: after all, any excess wealth that they create will be siphoned off in order to uphold the status quo. Only through innovation and, indeed, empire-building (in the economic and industrial sense of the word) can a society enjoy a greater measure of wealth.