For me, John Stewart Mill’s Harm Principle is a key element of libertarian philosophy. It holds that a person should be free to do as they like, until they start causing harm to others. If you want to have an avante garde theatre on your land, that is your right and I cannot object unless the noise is keeping me aware at 3:00am or you start dumping toxic paint into the river from which I drink.
At an election party the other night, however, I spoke with someone who has a more expansive libertarian philosophy than I had previously encountered – one that isn’t especially bothered by harm. They thought the important thing was for individuals to be as unrestricted as possible by government, even if their behaviour is causing harm to others. If you really value liberty for its own sake, perhaps it makes sense to adopt a Wild West ethical philosophy, in which individuals are behaving rightly whenever they try to get what they want. That said, I think this philosophy proves lacking very quickly as soon as some questions are asked.
Basically, the underlying ethic is that the strong should feel free to impose themselves on the weak. When you discard the Harm Principle, you leave people to fend for themselves. If my neighbour has guns and goons and I do not, I have no way to personally prevent him from dumping plutonium into my river, stealing my property, or having me beaten up for expressing my political views. In order to live in a decent society, I think we need to constrain the rights of the powerful. Everyone must be subject to the rule of law, and the law must protect important rights such as the freedom of speech.
A mega-libertarian society which discards the Harm Principle seems to me much like the Hobbesian state of nature. It wouldn’t necessary be quite as chaotic and violent as Hobbes believed, but it would certainly be terribly unjust. Without the Harm Principle, there is no moral basis to condemn rape, robbery, or murder. Under mega-libertarianism, a serial killer is just expressing themselves in their preferred manner, and the government really ought to get off their back.
I can appreciate the libertarian impulse to be skeptical about government and other systems of societal organization. At the same time, we must recognize that the whims of the over-mighty are also a major constraint upon liberty. It is much better to live in a democratic society with the rule of law than to live in a feudal society where military strength determines who is in charge and what the rules will be. In order for a society to be truly free, those who live within it need to adopt reasonable limits on their own behaviour.