The social and legal order of a libertarian society is strictly based upon “natural law.” Natural law, as it pertains to human society, is the complex of legal principles abstracted from the nature of man with the aid of reason. On the other hand, “positive laws” are laws imposed by decrees and legislative enactments of the state. It sometimes happens that positive laws coincide with the dictates of natural law, in which case they become superfluous. Compared with the socio-legal status quo, the natural law foundation stands to highlight the radical nature of libertarianism. Rothbard puts it as follows in The Ethics of Liberty: “The natural law is, in essence, a profoundly ‘radical’ ethic, for it holds the existing status quo, which might grossly violate natural law, up to the unsparing and unyielding light of reason.”
One way in which positive law endangers the liberty of individuals is by falsely imputing property rights to aspects of life which—seen from the point of view of natural law—are arbitrary. For instance, in regard to freedom of speech, the idea of defamation laws is premised on the false notion that the reputation of someone is his property, even though this reputation is strictly the outcome of subjective evaluation of other individuals.
The article posits that even though your reputation is yours, it is formed by other people and they own their own opinions. They can, thusly, market their opinions as such. If there is damage the remedy is in the natural law courts by juries. There would be no need for the state to impose arbitrary law, then.
But since no one can ever truly “own[”] the mind and attitude of another, this means that no one can literally have a property right in his “reputation.” A person’s reputation fluctuates all the time, in accordance with the attitudes and opinions of the rest of the population. Hence, speech attacking someone cannot be an invasion of his property right and therefore should not be subject to restriction or legal penalty. — Rothbard