"Aggression" versus "Harm" in Libertarianism
A discussion in the comments(archive) section of a post about blackmail brings up an issue about which many libertarians are confused. This concerns the idea of "harm." Libertarians often condemn "harming" others, and this is fine so far as it goes, if it is kept in mind that "harm" here is loosely meant as a synonym for aggression. But "harm" is really a broader category. Libertarianism says that only aggression may be countered with force, that aggression is the only way to violate rights so that a forceful response is justified. Other rightful behavior, even if it is immoral or "bad," is rightful so long as it is not aggression. (See my What Libertarianism Is, esp. notes 9-11 and accompanying text.)
"Committing harm" can also be rightful. Think of harm as a broader category that includes both harm-by-aggression, and other types of harm. This latter category is not an empty set. There are all sorts of ways you can "harm" someone that do not violate their rights. Competing with someone and "taking" his business, "stealing" his girl, beating him in a race--all may be viewed as harming him. But it's permissible to do this as it does not invade the physical integrity of his property--it does not commit aggression. It does not violate his rights. As can be seen in the blackmail debate above, by resorting to sloppy, fuzzy terms like "harm" all sorts of non-aggressive actions could be prohibited (such as blackmail, defamation, etc.). It thus leads to advocacy of unlibertarian laws.
One criticism, for exampe, that I had of Patrick Burke's otherwise insightful and interesting book No Harm: Ethical Principles for a Free Market (1994) was that he assumes causing harm can violate rights (see my book review in Reason Papers, in particular the section "Harm versus Aggression" at p. 138). Indeed, Burke's focus on harm leads him to view blackmail, defamation, and challenging someone to a duel as rights violations, since they "harm" someone.
Likewise, J.C. Lester's Escape from Leviathan: Liberty, Welfare and Anarchy Reconciled (2000) is problematic in focusing on actions that "impose costs" on others (see David Gordon and Roberta Modugno's review). Predictably, the use of a this fuzzy idea of "imposition of costs", as opposed to the libertarian notion of aggression, leads Lester to error as well--e.g., he supports intellectual property rights, even though he's an anarchist (he says, p. 96, that the lack of patent and copyright "will limit the incentive to produce memes"--groan).
So: libertarians should be careful in their concepts and terminology. Libertarianism upholds the right to be free from aggression--not harm. A similar consideration has led me to stop using the term "coercion" as a synonym for aggression; see my post The Problem with "Coercion". And we should also be careful in the use of metaphors--see Objectivist Law Prof Mossoff on Copyright; or, the Misuse of Labor, Value, and Creation Metaphors and Thoughts on Intellectual Property, Scarcity, Labor-ownership, Metaphors, and Lockean Homesteading.