The deeper motivation of anger was explored by psychologist Aaron sell in the January 2015, Psychology Today article. Sell asserts that the primary role of anger is preventing yourself from being exploited. If someone isn't treating you the way you expect, or is threatening your freedom and making you feel devalued; you start to become angry.
Often the primary motivation becomes setting someone straight, proving them wrong or teaching them a lesson.
Anger boosts confidence, optimism and risk taking. History has shown that many angry protests have accomplished change.
Anger fuels action and people pay attention. When you are sufficiently riled up you may actually think more clearly and present your ideas more forcefully. Your ability to suss out a strong and weak arguement may improve.
When angry, the heart rate increases, testosterone levels increase, cortisol levels decrease and our left brain is stimulated (emotions). When angry your body prepares to fight or flight. Everything is stimulated and the end goal is to resolve the condition. If not resolved, angry anticipation can create great health problems.
Thus angers physical response drives us to take action and resolve the conflict.