This is a question on which Judaism and Christianity disagree, as Yonason Goldson explains:
In an extraordinary example of human nobility, relatives of those killed in the Charleston massacre expressed their forgiveness for . . . the domestic terrorist who opened fire and took nine lives from the historic Emanuel A.M.E. church community. . . .
To be able to see past one’s own pain and find a mitigating factor to excuse violence is truly noble, even saintly. However, in the case of conscious, calculated evil, forgiveness may actually be a perversion of morality. Moral values should be so deeply rooted within that we can’t help responding to any violation of them with indignation and outrage. If we are truly committed to the values of good, how can we possibly tolerate evil, or those who do evil, especially when they do it in the name of good?
This is what the sages of the Talmud meant when they said, “Be discerning in judgment.” Look for every possible means of explaining away bad behavior. But after all is said and done, evil remains evil. Non-judgmentalism is an empty slogan that allows evil to proliferate unchecked.
What often gets lost in the discussion of forgiveness is the matter of accountability. If I break your window, my apology means nothing unless I’m willing to pay for the window. And if I’ve caused damage that can’t be repaired, punitive restitution may be the only means through which society as a whole can preserve respect for the rule of law and confidence in the institutions of justice. . . . . To take the life of any one person is, on some level, to take the life of every person. Justice must be served. Only then may it be possible to forgive.
Read more on Jewish World Review: http://www.jewishworldreview.com/0615/Goldson_Charleston_Massacre.php3