Thats missing the point. Dexters actions arent really gross except for the explicitly innocent people he has killed. But ignoring those instances, we are talking about a work of fiction, where Dexter is presented as an extremely competent law enforcement investigator and the viewer is presented with scenarios where a persons guilt of capitol crimes is assured and Dexter dispenses due justice. But Im talking about in real life, where vigilantism isnt the result of careful and methodical crime scene analysis, collecting evidence, and making a judgement. Its messy and perpetrated by people who are emotionally invested in vengeance, usually because they believe they have been personally wronged or have an ideological motivation.  These criminals may deserve to die. I wont get into the ethics of the death penalty, because thats also beside the point. Whether they deserve to die or not is irrelevant, vigilantism is gross because it doesnt follow a legitimate process, due process, to establish guilt or determine the proper consequence. Theres also zero accountability. If this was how justice was dispensed on a national scale, it would be an utter disaster of unbelievable proportions. As flawed as our current justice system is, vigilantism is several orders of magnitudes more flawed and would invariably result in innocent people getting killed, or people getting killed for minor offenses, etc. on a very large scale. Its fun to watch on tv, and we have all felt that certain criminals who got off light or got away completely deserve to be punished. And those feelings are valid, but it has to be done the right way that most accurately determines a persons guilt and gives the innocent a fair chance to defend themselves.