When someone goes outside the law to mete out a punishment for a crime, this is termed vigilante justice. The people involved in this type of justice are not qualified members of the judicial community, and they may break the law in the course of pursuing “justice.” People engage in this activity for a wide variety of reasons, ranging from perceived inactivity on the part of law enforcement to personal experiences, and many nations have very strict laws about vigilantism.
It is important to distinguish between vigilante justice and organized civilian crime fighting organizations. A Neighborhood Watch Association, for example, is not engaging in vigilantism, because the members are merely keeping an eye out for crime and reporting it to the appropriate authorities. By contrast, an angry mob which harasses someone suspected of molesting children is engaging in vigilantism, because it is making assumptions about the perpetrator of a crime, and going outside the legal system.
While some people defend vigilante justice, arguing that vigilantes step forward when the legal system is unable or unwilling to do its duty, this practice is highly questionable, and it has very sinister roots. It has been carried out for centuries, but it gained a great deal of momentum in the United States in 1800s with “Vigilance Committees,” which ostensibly fought crime, but actually persecuted immigrants and blacks. These committees attributed any form of crime to their minority of choice, conducting public lynchings and other forms of punishment in an attempt to frighten members of that minority out of town. In the American West, vigilante justice was also used as a tool to dispatch rivals, and anyone who owned substantial land or mineral claims was at risk of being executed by a vigilante mob under the direction of an acquisitive enemy.
The key problem with vigilante justice is that it lacks the organization of the bona fide legal system. While the wheels of justice can sometimes spin slowly, the legal system has a variety of measures in place which are designed to accurately identify criminals. Providing suspected criminals with a fair trial and an appropriate sentence is viewed as an important part of living in a civilized society, not least because it ensures that the right person is taken off the street.
In addition to lacking the protections of the legal system, vigilante justice often involves breaking the law. Humiliating, harassing, and killing people suspected of crimes is illegal, even if the suspect turns out to be the culprit. Members of a vengeance mob bent on vigilantism may also have personal connections with the crime, removing the element of neutrality from the case and making it difficult to separate personal emotions from genuine concerns about safety.