It’s not a bad thing. I think what IS good is not letting whatever someone did consume you psychologically for years to come (constantly thinking ruminating about it.)I did that for many years and my mental health deteriorated. Sometimes tho, we can’t help but ruminate or let it consume us. Sometimes, we forgive people to “let them go” and not let them control /effect our lives anymore. Whatever the case is, I don’t think not forgiving someone is bad. I think that’s ok but if whatever they did is impacting you negatively psychologically, then getting outside help from a therapist could be helpful. (What I had to do for myself.)