DEUT851 It should be noted that there is a fine line between the concept of "justice," which is always advisable and legitimate, and one who seeks "revenge," which always has negative connotations and is forbidden. Almost everyone who seeks revenge would not call it revenge, but "justice" carried out in order to correct how that person has been wronged. And seeking justice is certainly a Mitzvah (this verse]. Because of this rationalization that will become the mantra of anyone seeking revenge, that may be part of the reason why the Torah prohibited this sin altogether.