I've seen too many of my family members go through life hating people who wronged them. Was the hatred rightfully earned? Yes, in some cases it was. In other cases it was an issue of extreme personality conflicts, possible undiagnosed mental illnesses, childhood traumas, etc. Regardless of the cause, I've seen what hate does to people. Seeing the effects that this has on people has convinced me not to allow this to happen to me. Have people wronged me in life? Most certainly. I was a child in a mixed up household, with custody battles (nightmare from hell back in the 70s - unusual type of case for that time). I could rightfully claim to hate a number of people from this and other events in my life. However, it won't help me as a person to do so. It will turn me into a bitter old woman if I allow hate to take over my life.
Instead, I have learned to let go of the past -- and even forgive things that most people would have a hard time forgiving. Does it mean I've totally forgotten all of this? Of course not. That's not within the human realm, I don't think. However, when it does surface or someone brings it up it doesn't bring up feelings of anger. Sadness at times, perhaps, that I didn't have the joyous mother / father / family type relationship that others have. Sadness at times that I was not able to have a relationship with large numbers of family members while growing up (and never would have the same type of relationship, so don't seek it out now). However, hatred and anger? No. It would do no good for me to have this.
That said, letting go of the past and feelings of anger doesn't mean that you have to build a relationship with those people who have not been part of your life, even if it is through no fault of their own (I am not implying that is the case in this situation). Forgive and forget doesn't mean that you have to cozy up with the person and be their best buddy or have a relationship. Sometimes it is about allowing YOU to heal. You may bear scars but you can minimize their impact on your life.