John Stuart Mill's classic work ON LIBERTY provides most of libertarianism's theoretical foundation. One of Mill's most enduring contributions was his articulation of the boundary between between personal liberty and governmental interference. Mill basically argued we ought to be able to do whatever we want, as long as we do not harm others. But the so-called "harm principle" can be interpreted in many different ways, depending on what you mean by "harm." Mill's followers often use the term "self-regarding acts" and "other-regarding acts" to draw that boundary. Other regarding acts violate either the non-aggression axiom or property rights, while self-regarding acts do not. Unfortunately, Americans today have expanded the non-aggression axiom to cover miniscule harms, vague harms (psychological harms), and improbable harms. Our culture has expanded the non-aggression axiom to include a growing number of verbal harms; that is offensive verbiage. Mill argued that we can say whatever we want, short of falsely yelling "FIRE!' in a crowded theater. What he had in mind there is that the word FIRE could lead to a stampede for the exits, which could physically harm many of the theater patrons. We might expand that notion to include deliberately spreading false rumors about others, which damage the reputation. Of course, if it's true, then that's something else. Most recently, there has been a tendency to censor words that are highly likely to elicit physical retribution from the victim: so called "fighting words." The problem with expanding the non-aggression axiom to cover "fighting words" is that the tendency to react violently to words is culturally bound; that is, if we teach children to "punch out" anyone that calls them an offensive name (usually an ethnic slur), then we can expect an increase in aggressive behavior. Mill would have argued that we need to teach our children to have "thick skins" and to respond to verbal assaults verbally. "Sticks and stones will break my bones, but names will never hurt me!" We have also become overly generous in restricting other-regarding behavior in the context of property rights. Real libertarians argue that all rights are negative rights, which means that others (individuals and government) have a duty to NOT interfere with an individual's pursuit of private property via the transfer of property between individuals. The duty to not interfere is NOT the same as a duty to provide. Therefore, no one has a positive right to have anything apart from a mutually agreed upon contract. Therefore, I do not harm beggers by not giving them money. It is, after all, my money. On the other hand, if I choose to put a couple of dollars in a hat, that's OK too. But I do not have a duty to do it, and he does not have a right to expect it from me. Hence, I do not harm others by refusing to assist. So a good way to interpret the harm principle is to say that: "You can do whatever you'd like, as long as you do not violate the property rights of others, including the right of self-ownership.