"Righteous vengeance" refers to seeking revenge or punishment in a justified and morally acceptable way, typically in response to a wrongdoing or injustice. Full definition
When the state sets out to kill a killer, it becomes instead an actor in a drama about righteous vengeance. (firstthings.com)
Apparently Po is the only surviving member of his species, which makes him both the target of Shen's violence and an agent of righteous vengeance. (nytimes.com)
Understandably, others have greater difficulty overcoming a sense of betrayal or a desire for what seems like righteous vengeance against crime and corruption. (markreviewsmovies.com)