A man betrayed his spouse. A father abandoned his children. The police arrested an innocent women. An innocent man served jailed time. An officer abused his power. Minorities face unequal medical care, legal protection and education. Governments oppress cultural or religious groups. Women are being discriminated.
In these examples and others you feel resentful, angry and even furious as you realize the injustice and harm/destruction caused. You become motivated to protect the recipient from pain and suffering while holding the offending party responsible. You want to correct the wrongdoing and make it right.
Anger not only promotes justice, it can serve as a strategy that serves a positive purpose. The strategy is to change the world around us or to change ourselves to create alignment and harmony between the our internal word and our internal one