Also known as the Golden Rule and the Zero-Aggression Principle, The Non-Aggression Principle is considered by many in the Libertarian movement to be the core ethic of Libertarianism, however, working from first principles, with the origins of natural rights in the individual sapient mind evolving the capacity to articulate, and comprehend, the idea of "I think, therefore I own myself," that Self Ownership is the core ethic of Libertarianism, and the Non-Aggression Principle is but the most effective, rational, long term strategy for ensuring that a sapient individual's self ownership, and attendant natural rights that correlate to sapiency and self ownership, are respected by other sapient individuals and groups of sapients.
Strategy, Not Agency
As the most effective rational long term strategy for ensuring respect for one's self ownership and natural rights, the NAP satisfies both Utilitarian and Consequentialist arguments over the NAP, because self ownership removes the idea that the NAP is self existent self evident goal in and of itself. It also removes arguments about the NAP being dependent on some higher power to define good and evil and pass judgement upon sapients, as well as eliminates all claims as to the subjectivism of morality.
Non-Aggression Is Not Pacifism
While many pacifists would like to claim the NAP as their own, this simply is not the case.
Pacifism tolerates aggression by others, either against the individual, or against others, by others, committing only to not respond to aggression with violence. This is the antithesis to a commitment to oppose aggression, to refuse to tolerate aggression, to insist upon a non-aggressive society. The Non-Aggression Principle not only obligates the NAP practitioner to not aggress against others, but also to refuse to tolerate aggression by others, either against the practitioner as an individual, or additionally against others to varying extents (family, friends, strangers, community). Refusing to tolerate aggression by others, as individuals or groups, may take the form of public disapproval, shunning, civil action through dispute resolution, negotiation/diplomacy, or ultimately, responding to aggressive violence with defensive violence in response.
The Individual Choice to Respond to Aggression
To refuse to respond at all to aggression is tacit acceptance of aggression, and therefore, consent. Thus, "pacifism is objectively pro-fascist" (Orwell).
Practicing pacifism as a political tactic is only valid in a political system in which the polity, and its leadership, respect the moral scrupulousness of the pacifist and distain those who bully others to get their way. Thus, pacifism has been effective in the British Empire (Gandhi), and in the US (Martin Luther King Jr) and modern Europe (for the most part) because those cultures have a religious veneration for pacifism in the face of aggression, particularly in that such actions reflect upon ancient historical oppressions of christians in the Roman arena.
However, totalitarian regimes, like Nazi Germany, Soviet Russia, Communist China, North Korea, Pol Pot's Cambodia, and many muslim regimes like those of Nasser, Hussein, Arafat, and Saud, which have no cultural context of respect for pacifism, have proven to be nearly immune to the political pressure of such tactics.
Thus, the more rational long term strategy to ensure respect for self ownership and natural rights is to defend against aggression, proportionately but effectively to end such aggression. Thus the adversarial system of civil/common tort law positions plaintiff and defendant as adversaries of violator and violated, not equally innocent parties seeking compromise as in other legal systems that do not respect the objective invalidity of aggression.