I had a realization about hate quite a long time ago. When you hate someone, 99.999% of the time they don't know or they don't care. So the only one that ends up feeling bad 24/7 is you. You have to find a way to let it go and move on, forgiveness or not..
That's why it's important to "verbally" punish them on some level (if you hate them because they've done you wrong). They need to know, or if they've done wrong in a work/shared social context, then others need to know as well. Otherwise, it's as you said, only you feel bad and they have no idea or don't care.
Too much of the ills happening in the world today is (I would argue) due to us responding to bad things by appeasing, forgiving, or simply "letting it go" without confrontation/conflict.
