Is vigilante justice ever morally justified?

“In extreme conditions where the "rule of law" or the legislative, legal, and enforcement systems fail to provide proven justice without reasonable doubt, then it only follows that the only recourse is "vigilante justice" or "taking justice into one's own hands". This is not to claim, by any means, that this often happens. I can only conceive very rare cases.”

“I believe there are situations where someone could feel morally obligated to take the law into ones hands. The justification is with them. I'd love to hear your reasoning against it.”

“You're smuggling in the answer with "morally preferable to inaction." But that's a false binary. Inaction isn't your only alternative when systems fail—you have organizing, witness testimony, appeals, documentation, exposure, migration, resistance. These aren't vigilantism.”

“Your "justification is with them" is precisely the problem. If every person's internal conviction makes vigilantism moral, then the serial killer's certainty justifies their crimes equally. You've just demolished any objective moral standard. How do you distinguish righteous punishment from self-serving vengeance without external accountability?”