Why would they not be worthy of forgivess?
As Christine pointed out, there are several actions and behaviors that do not deserve to be forgiven. Some actions have so marked either a person or - indeed - the entire world that forgiveness is just not possible, nor should it be. It's easy to paint forgiveness up in flowers and play at some deep wisdom, but I find it unsatisfactorily empty. It's often painted up as "holding onto a hot coal" or some such nonsense, conveying the idea that we're only hurting ourselves in our "anger" towards that person, but that is not always the case. But even if it was, so what? It's not like people are usually enraged about these
niðingr day in and day out. Often they don't occupy much thought until the topic comes up. But why should their offense be given a pass, made to be "okay"?
You say that forgiveness is compassion towards many ills, but also evilness. Why does evil deserve compassion? An example (yes, I'm going to be that guy, and this is rhetorical; it's easy to type answers you don't actually mean): Few in today's world are actively or
actually angry at Hitler. Yet his actions were among the most evil that the 20th Century has ever seen. Why should he be forgiven? Why should the world let go of his actions?