Finally, there is the theory of Ethical Egoism. This theory proposes that the moral value of an action depends solely on the potential of the action to act in the long-term benefit of the actor. There are several arguments raised against the theory, but James Rachels proposes one as the key reason that Ethical Egoism is unacceptable. His rationale is that if a moral theory treats any group differently than another group solely based on an arbitrary characterization, then that theory is an unreasonable theory, violating the rule that an ethical theory should be founded on an objective basis.

There is, however, a defense that can be put up against this argument, by drawing a premise from Natural Law theory. In addition, the primary argument against Natural Law theory, the lack of a suitable value judgement to allow the derivation of what is in the universe to what ought to be in man's moral behaviors can be attacked in turn by using Ethical Egoism to provide for that value claim. As will be demonstrated, the two theories would seem to complement each other.

In the case of Ethical Egoism, the argument offered against it is that there is an injustice, and non-objective or discriminatory application of the theory. This seems an inherently reasonable claim about the theory, because it invariably divides any group of people into oneself, and all others for the purposes of determining ethical actions. However, when applied to the limiting case where all people are practicing ethical egoism, then everyone will base their actions on what will be to their greatest long-term benefit. Now, the greatest potential benefit to oneself will result not from exclusively selfish action, but from a balance of selfish and selfless acts. These selfless acts will be needed because it would seem that from observing behaviors of others practicing Ethical Egoism there is unlikely to be any benefit gained from those who do not benefit from you in return. Here, Aquinas' premise in Natural Law that we can determine the rightness of an action from its relationship to the observable natural laws in life comes in. The use of reason allows the Ethical Egoist to determine the way in which their fellow Egoists behave, and allows them to determine that a limited selfless act, something that could perhaps be judged wrong previously, is morally acceptable because Natural Law theory states that an action in accordance with reasoned derivation from observed natural laws is right. In the limiting case, where there is a perfect balance between selfish and selfless action by every individual in an ideal Ethical Egoist society, something of a Golden Rule pattern develops from reasoning action from observable personal behaviors.