The prohibition of revenge by the state is probably based on the premise that the state will make a correct decision on behalf of the victim - yes, it must be correct! If the state fails to perform this duty intentionally or negligently, and innocent people are wronged but the guilty are not punished, then must the innocent people suffer in silence? I don't think so. People who are innocent but are killed have the right to punish the wrongdoers. This is the right of an innocent person! Rather, it is the right of the deceased.
