"I have learned through bitter experience the one supreme lesson to conserve my anger, and, as heat conserved is transmitted into energy, even so our anger controlled can be transmitted into a power which can serve the world."
Jesus was angry with the money changers in the temple. He was made at the Pharisees and called them names like "you vipers" and "whited sepulchres".
Anger can be a mobilizing emotion. It gives us gumption to take action when we might otherwise overlook things and them go. Anger can be invigorating and give us strength in times of challenge. However, as Gandhi says, it must be conserved and controlled and channeled into constructive action, not acted out blindly.
When a person finally says "when enough is enough, that's enough" that person starts to move in a positive direction and finds his/her voice.
When a person says, "God damn it! I'm not taking this anymore!" it is time for change.
When have you wanted change bad enough that you were willing to initiate some action to make it happen and anger gave you the courage, the energy, the strength to start the work?