"So why are many on the alt-right former propertarians? For obvious reasons—neither are interested in liberty, neither are egalitarians. The social relations of property are authoritarian, dictatorial in fact, which have obvious appeal to fascists. The overlap between propertarians and fascism are more than the former would like to admit—particularly given how often the former have supported the latter. In short, both are authoritarians—but one hides their support for authoritarian social relationships under the rhetoric of 'liberty.'"—Iaian McKay (What it means to be libertarian)
Right-wing libertarians generally advocate negative liberty. They define liberty as the absence of coercive interference. Isaiah Berlin defined “negative liberty” as the absence of deliberate interference in one’s actions by others. Murray Rothbard’s conception of liberty differed from Isaiah Berlin’s definition of “negative liberty.” Rothbard’s concept of liberty is basically a form of negative liberty, but a form of negative liberty that I would call “propertarian liberty.” Some people, like Edward Cain and Iaian McKay, have argued that people with such a conception of liberty are actually “propertarians” rather than libertarians.
"Thus, Berlin's fundamental flaw was his failure to define negative liberty as the absence of physical interference with an individual's person and property, with his just property rights broadly defined."—Murray Rothbard (The Ethics of Liberty, Chapter 27)
Personally, I think this is a very bad way to define the term liberty. If one so defines liberty and also makes liberty the ultimate good, one would be forced to advocate things that are quite terrible. Rothbard's so-called "libertarian" theory of ethics logically leads to an extreme form of fascism.
Suppose that Mr Smith invites his neighbor, Mr. Jones, over to his house for a barbeque. While the burgers are cooking, Mr. Jones falls asleep while sitting in a chair in the driveway. While he is sleeping, Mr. Smith quickly takes bricks and builds a small prison around him, four walls and a roof, trapping him in. When Mr. Jones wakes up, he finds that he has been imprisoned by Mr. Smith. Mr. Smith has decided that he will hold Mr. Jones in this prison forever, until he dies. According to Rothbard’s libertarian theory of ethics, Mr. Smith has neither violated the rights of Mr. Jones, nor has he violated Mr. Jones’ liberty. In fact, Mr Jones would be violating Mr. Smith’s rights and transgressing against Mr. Smith’s liberty if he were to escape. Suppose that Mr. Jones knocks down the walls, breaks the roof to climb out, or breaks through the pavement below and tunnels out. Well, the pavement, the walls, and the roof are all the property of Mr. Smith, so Mr. Jones has no right to break free from this prison—if he breaks free from this prison, he has become the aggressor. Mr. Smith would be within his rights to hold Mr. Jones in captivity forever. Alternatively, Mr. Smith could tell Mr. Jones that he will release him if he signs a contract agreeing to transfer 100% of all his property, current and future, to Mr. Smith. Mr. Smith can then release Mr. Jones and effectively have a slave. All the work that Mr. Jones does will be solely for Mr. Smith’s benefit. Every bit of food gathered by Mr. Jones belongs to Mr. Smith, every bit of income that Mr. Jones earns is immediately transferred to Mr. Smith. According to Rothbardian theory, Mr. Smith has not violated any of Mr. Jones’ rights, and Mr. Jones’ liberty has not been taken away, since his property right was not violated but voluntarily transferred.
Suppose that a woman has a baby. She feels that the baby is a burden and decides that she wants to get rid of it. She decides to sit the baby in a box on the table and leave it there to starve. According to Rothbard, the mother is well within her rights. Furthermore, if anyone intervenes in order to either force the mother to feed her child or to take her child away, they have aggressed against her liberty. If the police break in to take her child from her, they have violated the mother’s rights. If they force her to feed the child, they have violated the mother’s rights. The appropriate course of action, according to Rothbard—if one cannot convince the woman to care for the child or voluntarily hand him/her over—is to do nothing and let the child die of hunger or thirst. No one has any right to violate the mother's liberty by coming in the house to save the child that she is neglecting! This, by the way, is not just my interpretation of the logical implication of Rothbard’s libertarian theory of ethics; this is Rothbard’s own interpretation of the implications of his libertarian ethics. Rothbard himself writes:
"Applying our theory to parents and children, this means that a parent does not have the right to aggress against his children, but also that the parent should not have a legal obligation to feed, clothe, or educate his children, since such obligations would entail positive acts coerced upon the parent and depriving the parent of his rights. The parent therefore may not murder or mutilate his child, and the law properly outlaws a parent from doing so. But the parent should have the legal right not to feed the child, i.e., to allow it to die. The law, therefore, may not properly compel the parent to feed a child or to keep it alive. (Again, whether or not a parent has a moral rather than a legally enforceable obligation to keep his child alive is a completely separate question.) This rule allows us to solve such vexing questions as: should a parent have the right to allow a deformed baby to die (e.g., by not feeding it)? The answer is of course yes, following a fortiori from the larger right to allow any baby, whether deformed or not, to die. (Though, as we shall see below, in a libertarian society the existence of a free baby market will bring such 'neglect' down to a minimum.)"—Murray Rothbard (The Ethics of Liberty, Chapter 14)
Another odd implication of Rothbardian liberty is a justification for monarchism. Suppose that Bitcoin is adopted as the official currency of all the governments in the world, sending the price of Bitcoin to the equivalent of over a million dollars per coin. Satoshi Nakamoto finds that he is now the wealthiest person on the planet. In fact, he is now so wealthy that he can afford to buy the whole world. And that is exactly what he decides to do. Satoshi buys all the land on the planet. Now, Satoshi owns the world. All the land belongs to him. He can now function as a sort of legitimate monarch. He can force everyone to pay rent to him in order to use his land. He can force everyone to obey any arbitrary rules he chooses. Since they are living in his world, they have to obey his rules. Upon Rothbard’s so-called “libertarian” theory of ethics, everyone in the world is still free even though everyone has to pay taxes to Satoshi and do anything that he tells them to. According to Rothbard’s libertarian ethics, Satoshi is well within his rights to collect taxes and require everyone on the planet to worship him as a condition of being permitted to exist on his land. If he becomes despotic and makes unbearable rules, he is still within his rights. Furthermore, no one would have the right to rebel against Satoshi’s rule since it is legitimately based on his justly acquired property rights. If the people rebel, they are violating Satoshi’s liberty. Furthermore, no one has a right to be on another person's property without their permission. Suppose that Satoshi tells a group of people that they are no longer welcome on his property. Well, Satoshi owns the world, so there is nowhere for them to go. Within a Rothbardian libertarian framework, Satoshi would certainly have the right to forcibly remove those people from the planet.
In recent years, we have seen many prominent anarcho-capitalists come out as fascists. Christopher Cantwell, for instance, now openly calls himself a fascist and flies an anarcho-capitalist flag with a swastika on it. In my article Thoughts on the Alt-Right, I explained some of the other reasons that anarcho-capitalists tend to gravitate towards fascism. In addition to the reasons that I mentioned there, anarcho-capitalists tend to gravitate towards fascism simply because they define liberty in an extremely authoritarian way.