Vigilantes exist on a continuum that has death squads and lynch mobs at one end and political terrorists at the other. Somewhere in the middle comes the private citizen who thinks he can do better than the police. In fiction we allow him to prove his case- and several actors- most recently Liam Neeson- have profited from our indulgence- but in reality he's usually an incompetent who winds up killing people (often of a different ethnicity) who weren't any kind of threat.
The fiction is Batman, the reality is Bernhard Goetz.
