I always wonder how moral and fair it is to provide an opportunity for rehabilitation to someone guilty of a heinous crime, since they didn't provide a second c

I always wonder how moral and fair it is to provide an opportunity for rehabilitation to someone guilty of a heinous crime, since they didn't provide a second chance to their victims. It seem like a great cosmic injustice. As for punishing vigilantes, should settling the score be more severely punished than the original crime? Let's say a person kills someone I love, and I take my revenge by killing them, am I now not worthy of rehabilitation?