Forgiveness can be unwise if you are in a teaching position. One of my sons was particularly heedless when he was four years old. When he ran across the street, I spanked him because he could understand a spanking much better than he could understand the prospect of getting run over. In that situation, he was better off being punished than being forgiven. But one of the things I want to teach my children is forgiveness.
Forgiveness is sometimes unwise.
If the magistrates of a civil society allow the guilty to go unpunished, the innocent will be oppressed. Magistrates must be more concerned with justice than mercy. Justice requires that all debts be paid in full. My being a mature, responsible member of society requires the same thing. The only problem is that sometimes, with the best will in the world, we cannot pay our debts.