You stop the fool from committing wrongful deeds out of love for him as well. Living under God's grace does not mean never standing up for what's righteous or truthful. But the moment you go beyond ceasing the wrongdoing, or if you introduce hatred and revenge to the equation - you reduce your spiritual self. This is a very big ask, from anyone, but if you can allow yourself to truly feel no hatred while putting an end to suffering - you won't have this inner turmoil anymore. Out of love, you can stop your fellow man from committing misdeeds. You can allow him the gift of isolation and humanity in order for them to at least consider giving good to the world, regardless of the fact that they're not able to make up for what they've done in this lifetime. It's exactly the people who sin against others and themselves to such degrees that deserve the most mercy. Because they are the ones who are truly in need of it. Without that mercy, they will further cast themselves into darkness - destroying themselves and others in their wake. And by destroying them yourself - they have won, because now you have cast yourself into that same darkness that created them in the first place. You cannot forget the sanctity of your own soul when dealing with the darkness of others. Fighting is done for protecting, for preserving, for neutralization. The very moment you begin fighting for revenge, hatred, mercilessness, punishment - is the moment you've lost. Because this is exactly what the enemy would want. It wants to multiply itself through you, and through the corruption it has incited within you.