Anger is an emotion that serves a limited purpose, and those benefits and uses are solely restricted to the moment at hand. Anger is a biological directive intended to motivate us to stand up for life and liberty. If someone is bludgeoning your child to death on the sidewalk, nature wants you to become angry about that, so that you intervene to protect your offspring. Anger is a response to any type of threat, whether real or imagined.
When we hold onto anger, however, anger becomes our own worst enemy. It is capable of tearing apart our lives more efficiently than most outside tormenters ever could. Humans have thrown a quark in nature’s anger mechanism. Our higher cognitive abilities and knack for thinking of and dwelling on the future, combined with our complex social structure and extraordinary ability to allow abstract and often meaningless beliefs to govern our lives, means the anger mechanism has gone a little haywire in our species. When a buffalo gets angry, its anger is short-lived, and dissipates once the lion goes away. But humans dwell on their anger, carrying it around with them for weeks, months, years, or even lifetimes.
Anger is not wrong just because it is destructive. It's also wrong because in most social situations it's incorrect, inaccurate, unjustified, and driven by a distorted perspective. Oh, sure, our anger always feels justified. In truth, it never is. (Yes, never.) Even when we are in the right about the wrongfulness of a particular action (and even this we get wrong more often than we presume); we are never 100% right about the intent of the perpetrator (which we could never know) or the degree to which we become angry (which is by nature programmed to be extremely over-reactive).
People are skilled practitioners when it comes to hurting each other. Yet the most frustrating truth underlying this bitter fact is that most people never set out to hurt others. People aren’t trying to be evil. Even Hitler himself was not an "evil" person, just a confused little man whose personal beliefs, convictions, and insecurities led him to commit atrocious acts. People rarely hurt each other because they desire to bring more suffering into this world. They do some because of several very down-to-earth reasons:
A) We hurt each other because we are all imperfect people acting in imperfect ways, without the gift of foresight to see the future and predict beforehand the potential hurtful effects of our actions.