Forgiveness does not preclude or cancel out justice. St Paul's argument in the book of Romans, in some measure, is the revelation of the "righteousness" or "justice" (same word in Greek) that is revealed in the crucifixion of the Messiah, where our forgiveness is found. To forgive, in the deepest sense of the term, is to release (aphiami): we have been held in bondage by the one the Scriptures call the evil one, the devil, the serpent, the dragon, or the satan (yes, there is always a definite article). The Cross releases us, forgive us, from our sins by which we were held in slavery to death and unrighteousness. Since the serpent had no legitimate claim on us (he gained power by deceit and fraud), God's justice is our forgiveness.
Of course, this goes further and deeper. "Forgive everyone for everything." Let's not hold each other in bondage, but release others as we have been released, just as we pray in the prayer given to us by our Lord: "forgive us our debts/trespasses, as we forgive our debtors/those who trespass against us." Forgiveness is the Kingdom come into our midst now; it is also the great promise of the Kingdom come in its fullness.