The Second Brahma Vihara practice, karuna, is an essential complement to the first, metta. Metta directs energy toward enabling beings to be happy; karuna intends relief for their suffering. It seems to me when you combine them you have what Jesus meant when he talked about "love."
Sympathy, empathy, compassion, pity, mercy.... How do we relate to suffering? What is the quality of our acquaintance with it, how do we understand it, what do we do about it?
In a group discussion, some women said they couldn't imagine having compassion for certain types of people. But in my understanding, we need to work for compassion for everyone.
The reason for compassion toward people who do terrible things is that they did them from a failure of compassion toward the people who first did terrible things to them.
If I can't have compassion for someone, I tend to blame them -- seeing no responsibility for the tragedy anywhere else -- perhaps even demonize them, seeing them as wholly evil. Then I can level retribution at them safely without seeing that I in turn am acting hurtfully/with violence/evilly, projecting my fears onto them and exorcising them by "punishing" my victim -- who may be the original person who harmed me, but all too often is another I project evil onto, so I may "get back at" the world. This is the vicious circle that is responsible for war.
When a child is hurt in this way, it is worse, for it is harder for the child to come to terms with how the world has failed to nurture. Adults teach the child to ignore, suppress and deny the reality, with the result that the wounds fester in the unconscious, hurting the child's self-esteem and grasp of reality. When such victims finally find their own victims, the damage they wreak is worse than the damage from people who had nurturing childhoods.
Compassion doesn't mean we avoid appropriate action toward a perpetrator. And it doesn't necessarily mean we are not angry at or fearful of such evil. But it does mean we grieve for the fact that anyone is ever hurt in this way, and it means we try to act in such a way as to stop the vicious circle.
Alice Miller has written extensively on this vicious circle and its prevalence in our culture. For Your Own Good is a good book to start with.
When I find myself feeling anger, resentment, fear, and/or hatred toward someome, I try to remember to say "May [name] be free from harm. May he enjoy mental well-being. May he enjoy physical well-being. May he enjoy ease of livelihood." For if an evil-doer becomes free of the danger of both physical harm and the harm he causes himself by his own ignorance, greed and hatred -- and becomes sane enough to enjoy true mental well-being -- then he will abide in the natural love of all beings that comes from perceiving our essential interconnection, and work for their good.
And if I can remember this essence, and care about his connection to it, then my actions will spring from this love, and help heal not only him but myself and the world.