Violence is the use of physical force against a person or persons without their consent. Typically, the use of violence is for establishing control over a situation, as when a robber pulls a knife on a victim, or the victim pulls a gun on the robber.
Threats of violence, especially threats that are credible to the recipient, are sometimes included in the definition of violence, because they have the potential to coerce and therefore deprive the person of liberty to do what he wanted to do. However, there is controversy about exactly what sort of threats warrant defensive violence; The Ethics of Liberty argues that it is important to insist "that the threat of aggression be palpable, immediate, and direct; in short, that it be embodied in the initiation of an overt act. Any remote or indirect criterionâ€”any 'risk' or 'threat'â€”is simply an excuse for invasive action by the supposed 'defender' against the alleged 'threat.'" Fraud is also sometimes considered equivalent to aggression, in that it does not create valid legal title to the property obtained by that means.
 Aggression and self-defense
Aggression is unjustified violence. While violence is a concept that can be objectively determined, aggression is subjectively determined. What one person calls aggression, another may regard as self-defense or defense of others. Revolutionary violence, for example, is denounced as criminal by the government but may be viewed as heroic by the rebels' supporters. Likewise, the government's action in arresting those who commit victimless crimes is regarded as justified by those who believe that a democratically elected government's laws should be obeyed, regardless of their merit.
Violence is sometimes viewed as justified on the grounds of negative externalities. According to this theory, certain behaviors must be deterred through violence because they would harm people's rights to a "fair" social order. There may be a lengthy and uncertain chain of causation that is used to justify the violence; for example, the argument is sometimes made that cannabis possession should be illegal because a person who uses it might neglect a child or get in an automobile accident. Preventing this possible harm is deemed more important than the rights of those who would have used drugs in a relatively responsible way. A similarly questionable chain of cause-and-effect was used by FBI special-agent-in-charge Owen Harris to justify suppressing coins made of real silver, because they are supposedly more "fake" than the government's fiat money: "People understand that there is only one legal currency in the United States. When groups try to replace it with coins and bills that donâ€™t hold the same value, it affects the economy. And consumers were using their hard-earned money to buy goods and services, then getting fake goods in return."
Utilitarians attempt to weigh the costs and benefits of violence in deciding whether it is justified. The problem is that, as Henry Hazlitt points out in Economics in One Lesson, it is very easy to fall prey to the fallacy of the broken window by failing to take into account all the effects of violent intervention. Although Rothbard favored deontological over consequentialist arguments, he devoted Chapter 12 of Man, Economy, and State to the economics of violent intervention in the market, examining the negative consequences, both intended and unintended, of various types of government actions. The government's monopoly on large-scale organized violence within its territory is its defining characteristic, and Rothbard defined political theory as "the important subset of moral theory that deals with the proper role of violence in social life."
Advocacy and threats of violence are regulated by the State. It is legal for citizens to advocate that the government institute a program of violence against a certain group, and to vote for that program; but it can be considered sedition, treason, incitement to illegal violence, or another form of illegal conspiracy if citizens advocate anti-government violence and form a group to carry out that agenda. It is also legal for the government to threaten to arrest citizens if they engage in certain behavior, but it is illegal for the citizens to respond in kind by threatening violence against government officials. Hence, for example, the arrest of hedge fund manager Vincent P. McCrudden for making death threats against Securities and Exchange Commission leaders. Rothbard stressed the importance of distinguishing between being a conspirator or criminal mastermind and merely exhorting violence without having anything further to do with criminal activities. In his view, since every man is free to adopt or not adopt any course of action he wishes, the person exhorting violence is not responsible for the violence committed; â€œ'Inciting to riot,' therefore, is a pure exercise of a manâ€™s right to speak without being thereby implicated in crime."
Rothbard also points out, "The gravest crimes in the Stateâ€™s lexicon are almost invariably not invasions of person and property, but dangers to its own contentment: for example, treason, desertion of a soldier to the enemy, failure to register for the draft, conspiracy to overthrow the government. Murder is pursued haphazardly unless the victim be a policeman, or Gott zoll hÃ¼ten, an assassinated Chief of State". The U.S. Sentencing Guidelines specify that treason is punishable by life imprisonment. They also specify that failure to register for the draft during a time when persons are being inducted for compulsory military service is punishable at offense level 12, which for a first-time offender would carry 10-16 months in prison. They also specify that if a crime is committed against a current or former government officer or employee or his immediate family member, and the offense is motivated by that status, then a major increase in the prison sentence, possibly a doubling or more, is applicable. 10 U.S.C. Â§ 885 specifies death or any punishment less than death as the penalty for desertion during war.
 Relation to contract
Ludwig von Mises regarded the progress toward high civilization as depending on the substitution of relations based on contract for relations based on violence. Violence can sometimes be used to enforce a contract, as when hired muscle is used to repossess property in settlement of a debt, or physical harm is threatened against the debtor if he does not pay. Statists sometimes point to an implied social contract that they believe should be enforced by violence if necessary.
Sometimes nonviolent alternatives are available to encourage adherence to social norms. Blacklisting and ostracism, for example, serve to protect people from those who are known to have a history of misconduct. These methods also punish the violator by making it more difficult or costly for him to engage in transactions, since other participants in the marketplace may require a premium to compensate for the risk of dealing with him, if they are willing to deal with him at all. According to Murray Rothbard, merchants in the Middle Ages relied on ostracism and boycotts before arbitration decisions were legally binding. The person who ignored an arbitrator's award would not be able to avail himself of an arbitrator's services until he made good on his debt. Rothbard opines, "Nowadays, modern technology, computers, and credit ratings would make such nationwide ostracism even more effective than it has ever been in the past."
- Rothbard, Murray. "Self-Defense". The Ethics of Liberty. http://mises.org/rothbard/ethics/twelve.asp.
- "Speaking Out Against Drug Legalization". DEA. http://www.justice.gov/dea/demand/speakout/05so.htm.
- FBI (5 April 2011). "Private Tender". http://www.fbi.gov/news/stories/2011/april/dollar_040511.
- "The Lesson". http://www.fee.org/library/books/economics-in-one-lesson/#0.1_L2. "[T]he whole of economics can be reduced to a single lesson, and that lesson can be reduced to a single sentence. The art of economics consists in looking not merely at the immediate but at the longer effects of any act or policy; it consists in tracing the consequences of that policy not merely for one group but for all groups. Nine-tenths of the economic fallacies that are working such dreadful harm in the world today are the result of ignoring this lesson. Those fallacies all stem from one of two central fallacies, or both: that of looking only at the immediate consequences of an act or proposal, and that of looking at the consequences only for a particular group to the neglect of other groups."
- Rothbard, Murray. "Decay from Within". For a New Liberty. http://mises.org/rothbard/newlibertywhole.asp. "Current free-market economics is all too rife with appeals to gradualism; with scorn for ethics, justice, and consistent principle; and with a willingness to abandon free-market principles at the drop of a cost-benefit hat."
- Rothbard, Murray. "The Economics of Violent Intervention in the Market". Man, Economy, and State. http://mises.org/rothbard/mes/chap12a.asp.
- Rothbard, Murray N. (1979). "Myth and Truth About Libertarianism". LewRockwell.com. http://www.lewrockwell.com/rothbard/rothbard168.html.
- Weidlich, Thom (23 March 2011). "Hedge Fund Manager Jailed for Death Threats Says Regulators Out to Get Him". Bloomberg. http://www.bloomberg.com/news/2011-03-23/ex-fund-manager-charged-in-sec-death-threat-blames-retaliation-for-plight.html.
- Rothbard, Murray. "War, Peace, and the State". Egalitarianism as a Revolt Against Nature, and Other Essays. p. 131. http://library.mises.org/books/Murray%20N%20Rothbard/Egalitarianism%20as%20a%20Revolt%20Against%20Nature,%20and%20Other%20Essays.pdf.
- "U.S.S.G. Â§2M1.1 â€” Treason". U.S. Sentencing Guidelines. U.S. Sentencing Commission. 2011. http://www.ussc.gov/Guidelines/2011_Guidelines/Manual_HTML/2m1_1.htm.
- "U.S.S.G. Â§2M4.1 â€” Failure to Register and Evasion of Military Service". U.S. Sentencing Guidelines. U.S. Sentencing Commission. 2011. http://www.ussc.gov/Guidelines/2011_Guidelines/Manual_HTML/2m4_1.htm.
- "Sentencing Table". Federal Sentencing Guidelines Manual. 2011. http://www.ussc.gov/Guidelines/2011_Guidelines/Manual_HTML/5a_SenTab.htm.
- "U.S.S.G. Â§3A1.2 â€” Official Victim". U.S. Sentencing Guidelines. U.S. Sentencing Commission. 2011. http://www.ussc.gov/Guidelines/2011_Guidelines/Manual_HTML/3a1_2.htm.
- von Mises, Ludwig. "Violence and Contract". Socialism. http://mises.org/books/socialism/part1_ch.1.aspx#_sec2.
- Rothbard, Murray. "The Courts". For a New Liberty. http://mises.org/rothbard/newlibertywhole.asp.