In an imaginary construction of a world inhabited by a single being, it is possible that the pursuit of morality is the same as the pursuit of self-interest in that what is good for the agent is the same as what is in the agent's interests. Arguably, there could never arise an occasion when the agent ought not to pursue self-interest in favor of another morality, unless he produces an alternative ethical system in which he ought to renounce his values in favor of an imaginary self, or, other entity such as the universe, or the agent's God. Opponents of ethical egoism may claim, however, that although it is possible for this Robinson Crusoe type creature to lament previous choices as not conducive to self-interest (enjoying the pleasures of swimming all day, and not spending necessary time producing food), the mistake is not a moral mistake but a mistake of identifying self-interest. Presumably this lonely creature will begin to comprehend the distinctions between short, and long-term interests, and, that short-term pains can be countered by long-term gains.
In addition, opponents argue that even in a world inhabited by a single being, duties would still apply; (Kantian) duties are those actions that reason dictates ought to be pursued regardless of any gain, or loss to self or others. Further, the deontologist asserts the application of yet another moral sphere which ought to be pursued, namely, that of impartial duties. The problem with complicating the creature's world with impartial duties, however, is in defining an impartial task in a purely subjective world. Impartiality, the ethical egoist may retort, could only exist where there are competing selves: otherwise, the attempt to be impartial in judging one's actions is a redundant exercise. (However, the Cartesian rationalist could retort that need not be so, that a sentient being should act rationally, and reason will disclose what are the proper actions he should follow.)
If we move away from the imaginary construct of a single being's world, ethical egoism comes under fire from more pertinent arguments. In complying with ethical egoism, the individual aims at her own greatest good. Ignoring a definition of the good for the present, it may justly be argued that pursuing one's own greatest good can conflict with another's pursuit, thus creating a situation of conflict. In a typical example, a young person may see his greatest good in murdering his rich uncle to inherit his millions. It is the rich uncle's greatest good to continue enjoying his money, as he sees fit. According to detractors, conflict is an inherent problem of ethical egoism, and the model seemingly does not possess a conflict resolution system. With the additional premise of living in society, ethical egoism has much to respond to: obviously there are situations when two people's greatest goods the subjectively perceived working of their own self-interest will conflict, and, a solution to such dilemmas is a necessary element of any theory attempting to provide an ethical system.
The ethical egoist contends that her theory, in fact, has resolutions to the conflict. The first resolution proceeds from a state of nature examination. If, in the wilderness, two people simultaneously come across the only source of drinkable water a potential dilemma arises if both make a simultaneous claim to it. With no recourse to arbitration they must either accept an equal share of the water, which would comply with rational egoism. (In other...