Final answer:
Ethical egoism dictates that it is never morally permissible to act against one's self-interest. Strong ethical egoism affirms self-interest as the highest moral obligation, making it incompatible with ethical conflict-regulation and interpersonal relationships where mutual benefit and compromise are necessary. It faces substantial objections due to its limitations in addressing collective welfare.
Step-by-step explanation:
If ethical egoism is true, then it is never morally permissible for someone to sacrifice their own interests for the sake of others. Ethical egoism, particularly strong ethical egoism, argues that it is always right to act in one's own self-interest, and it is morally wrong to do otherwise. If everyone acted upon this moral principle, it would preclude ethical conflict-regulation and interpersonal authoritative regulation, as it would imply that actions against one's interests are sometimes morally required.
Furthermore, ethical egoism cannot consistently support the act of killing one's grandfather for inheritance benefits as it creates an ethical conflict between self-interest and the interest of another. It lacks a sound moral guideline to regulate such conflicts; hence it does not hold up as a universal moral theory. Ethical egoism also rejects the idea of treating people purely as means to an end, as every person is an end within themselves.
The concept of ethical egoism is often juxtaposed with altruistic ideologies and criticisms, stating that no single individual can expect the whole world to confer maximum benefit to them alone, and the expectation of such is unreasonable. This highlights the limitations of ethical egoism in addressing collective social welfare and interpersonal ethical dilemmas.