The vigilante is a person who punishes crime independently of the authority of the state. The term comes from the phrase "vigilance committee", which described organized vigilantes in the 1800s United States. The vigilante also appears commonly in fiction. Arguments against vigilantes are that they violate the will of the majority which the is put into effect through the State; if the majority wished to punish an offender, then they would have done so through the police and courts. In cases in which public opinion polls or other measures of the people's will show that the majority is on the side of the vigilante, the anti-vigilante argument then shifts to the right of the accused to have a trial to determine whether he really is guilty or innocent.
In cases in which the evidence clearly shows that the accused is in fact guilty and that the only way a trial would acquit him would be through miscarriage of justice, the argument then shifts to the dangerousness of allowing people to unilaterally make their own decisions of what constitutes justice, or for one powerful individual or group to exercise such power, even if it is on behalf of the people. Of course, this raises the question of what makes the government a better avenger on behalf of the people than a vigilante; or, if courts are the means by which the accused is protected from mob rule, what makes the court — whose rulings are made by politically-connected judges or ordinary citizens (usually members of the masses, since prosecutors typically try to eliminate any intellectuals from the jury pool) serving on juries — a better decision maker than a superhero, who may have special powers or greater intelligence with which to discern the truth, and who can dispense with bureaucratic red tape.
Then, of course, there are other arguments that could be raised on behalf of the vigilante: What if the people who are against the vigilante favor his superordinate goals — e.g. justice, freedom from crime, and so on — but are mistaken in their beliefs of how those goals can best be achieved? What if his opponents in government and the media are most concerned with protecting their own positions rather than with the good of the rest of society? What if the government, because of the flaws in democracy or the venality of the rulers, is a worse custodian of power than the vigilante? Also, the vigilante generally uses his own resources to punish offenders, while the government forcibly takes money from the innocent to fund its agencies.