Natural law theorist Murray Rothbard traces the non-aggression principle to natural law theorist St. Thomas Aquinas and the early Thomist scholastics of the Salamanca school. This, in turn, may be seen in relation to Aquinas’ view on greed, “a sin against God, just as all mortal sins, in as much as man condemns things eternal for the sake of temporal things”, and on envy, which be defined as “sorrow for another’s good” (cf. Seven deadly sins).
Early formulations that use terms such as “harm” or “injury,” such as those of Epicurus and Mill above, are today generally considered imprecise. “Harm” and “injury” are too subjective; one man’s harm may be another man’s benefit. For example, a squatter may make “improvements” that the owner considers detrimental. Modern formulations avoid such subjectivity by formulating the NAP in terms of individual rights or observable conduct (initiation of force/violence).
In modern social-political culture advocating civil liberties, laissez-faire markets, and limited government, i.e. by the US Libertarian Party (US LP) and by Young Americans for Liberty (YAL), similar formulations of NAP are commonplace (see the libertarian pledge).
I feel I must add this from the Libertarian Platform:
“We hold that all individuals have the right to exercise sole dominion over their own lives, and have the right to live in whatever manner they choose, so long as they do not forcibly interfere with the equal right of others to live in whatever manner they choose.”
In this alone we observe the Reason which necessitates abandoning all GOVERNments of Force, replacing those with a Voluntary System in which this Axiom is the primary and essential Principle.
All Humans have and must have their Right to Life, for without Life there is Nothing. Life is the Property only of oneself and of No Other. It follows that each human thus has the right to Sustain his life, to seek happiness and prosperity. It also follows that no human may intrude upon or Sacrifice any part of the Life of any other. for one thereby cedes his own Right to Life.
Does this not negate all Governments of Force, and thereby the Rulers who rise to enForce those against all others?