Cowardice is wholly inconsistent with non-violence. Translation from swordsmanship to non-violence is possible and, at times, even an easy stage. Non-violence, therefore, presupposes ability to strike. It is a conscious deliberate restraint put upon one's desire for vengeance. But vengeance is any day superior to passive, effeminate and helpless submission.
Forgiveness is higher still.
Vengeance too is weakness. The desire for vengeance comes out of fear of harm, imaginary or real. A dog barks and bites when he fears. A man who fears no one on earth would consider it too troublesome even to summon up anger against one who is vainly trying to injure him. The sun does not wreak vengeance upon little children who throw dust at him.