There seems to be a lot of confusion about the concept of “natural rights,” not only among the anarcho-left, but also among some radical libertarians. Natural rights are claimed to be some kind of mystical, inherent code that just kind of magically exists out of thin air.
Murray Rothbard denied that natural rights are based on mysticism, however.
Natural law theory rests on the insight that we live in a
world of more than one—in fact, a vast number—of entities, and that each
entity has distinct and specific properties, a distinct “nature,” which can be
investigated by man’s reason, by his sense perception and mental faculties...
…the nature of man is such that each individual person
must, in order to act, choose his own ends and employ his own means in
order to attain them. Possessing no automatic instincts, each man must
learn about himself and the world, use his mind to select values, learn
about cause and effect, and act purposively to maintain himself and
advance his life. Since men can think, feel, evaluate, and act only as
individuals, it becomes vitally necessary for each man’s survival and
prosperity that he be free to learn, choose, develop his faculties, and act
upon his knowledge and values. This is the necessary path of human
nature; to interfere with and cripple this process by using violence goes
profoundly against what is necessary by man’s nature for his life and
prosperity. Violent interference with a man’s learning and choices is
therefore profoundly “antihuman”; it violates the natural law of man’s
needs. (For a New Liberty, p.27)
Ayn Rand had a similar perspective:
The source of man’s rights is not divine law or congressional law, but the law of identity. A is A—and Man is Man. Rights are conditions of existence required by man’s nature for his proper survival. If man is to live on earth, it is right for him to use his mind, it is right to act on his own free judgment, it is right to work for his values and to keep the product of his work. If life on earth is his purpose, he has a right to live as a rational being: nature forbids him the irrational. Any group, any gang, any nation that attempts to negate man’s rights, is wrong, which means: is evil, which means: is anti-life.
(For the New Intellectual, p.182)
Thus, for every individual, a right is the moral sanction of a positive—of his freedom to act on his own judgment, for his own goals, by his own voluntary, uncoerced choice. As to his neighbors, his rights impose no obligations on them except of a negative kind: to abstain from violating his rights.
The right to life is the source of all rights—and the right to property is their only implementation. Without property rights, no other rights are possible. Since man has to sustain his life by his own effort, the man who has no right to the product of his effort has no means to sustain his life. The man who produces while others dispose of his product, is a slave.
(The Virtue of Selfishness, p.93)
As David Gordon has explained, natural-rights libertarianism can be boiled down to a very simple principle: that slavery is wrong. (Also see Wendy McElroy's take on the subject, here.)
When prodded, the idiots who claim that rights and morality don’t exist always—ALWAYS-- end up caving in. The second they concede that rape or murder is wrong, their claim goes out the window.
In other words, they are mostly attention whores trying to sound 'intellectual.' Francois Tremblay considers them trolls. And they are.
Natural rights are the best foundation for market anarchism. As Rothbard pointed out,
Not only had natural law and natural rights given way throughout society to the arbitrary rule of utilitarian calculation or nihilistic whim; but the same degenerative process had occurred among libertarians and anarchists as well. Spooner knew that the foundation for individual rights and liberty was tinsel if all values and ethics were arbitrary and subjective.
Yet, even in his own anarchist movement Spooner was the last of the Old Guard believers in natural rights; his successors in the individualist-anarchist movement, led by Benjamin R. Tucker, all proclaimed arbitrary whim and might-makes-right as the foundation of libertarian moral theory. And yet, Spooner knew that this was no foundation at all; for the State is far mightier than any individual, and if the individual cannot use a theory of justice as his armor against State oppression, then he has no solid base from which to roll back and defeat it.