After all, he knows that God forgave him, sinner that he is. The forgiving person never hopes to see another condemned to Hell. Like God, he hopes that all will eventually convert, no matter how hardened their hearts may be at the present time. Above all, the forgiving person helps to propagate the kingdom of God. Hell is none other than ultimate despair, ultimate selfishness.
Many people are already there.
Our own acts of forgiveness may be the light of the Kingdom for many a soul, the light that may liberating them to the way of holiness - before it is too late.