To forgive or not to forgive?
There is power in the act of forgiveness. If a group of people continually attempts to punish someone that has done something they feel is wrong, that person will continually try to fight them - perhaps resorting to ever more extreme acts, which can hurt society even more.
However, what if the person is unrepentant? It means the person is still a risk to society - this is perhaps why society isn't usually very forgiving of those it deems to be criminals. Either the alleged criminal has to change or society has to change to accept that person's behavior.
On the other hand, if the person is repentant, renounces his past behavior, and works actively to prevent others from engaging in the same behavior or having to suffer the results of similar behavior, then forgiveness can easily turn two former opponents into allies.
If you have a society that forgives one group of unrepentant criminals, but not another - or one group of repentant criminals, but not another - then you are setting up a double standard. You are basically saying those who are forgiven are above the law, while everyone else has to suffer the law's consequences. Actions like these undermine the very legitimacy of the justice system.