We are not permitted revenge. There you have it plainly. People who are Christian, people who are called friends of Jesus, are simply people who love even when love goes against every worldly instinct and every action deemed acceptable and even normal by society. Then he says clearly that if we love him, we live in that love with all of our being in every way every day of our lives. Loving others is, in fact, the response to God's love and simultaneously the mark of being a Christian.
Christians love others.
It's part of the definition given by God. Different groups of people are known for different attributes or ways of acting. Those in the military are bound by a code of honor and behavior. If that is seriously broken, the person is released from being part of the military, oft times, dishonorably discharged. Acting according to code is not an option in the military, it's required.