Henepola Gunaratana writes in Mindfulness in Plain English,

For all practical purposes, if all of your enemies are well, happy and peaceful, they would not be your enemies. If they are free from problems, pain, suffering, affliction, neurosis, psychosis, paranoia, fear, tension, anxiety, etc., they would not be your enemies. Your practical solution towards your enemies is to help them overcome their problems, so you can live in peace and happiness. In fact, if you can, you should fill the minds of all your enemies with loving kindness and make all of them realize the true meaning of peace, so you can live in peace and happiness. The more they are in neurosis, psychosis, fear, tension, anxiety etc., the more trouble, pain, and suffering they can bring to the world. If you could convert a vicious and wicked person into a holy and saintly individual, you would perform a miracle. Let us cultivate adequate wisdom and loving kindness within ourselves to convert evil minds to saintly minds.