Anger is a very appropriate and necessary response to an injustice. But stand back now; the truth, clearly spoken, is always your best weapon. Calmly spoken, it can burn a hole through the hardest heart. - Bill Chickering

There are times when one must make an impassioned stand, but I think those instances are few and far between. Most of the time, by making your position with integrity and with compassion, you allow the other person to reconsider their position, and you avoid what might prove to have been an entirely unnecessary confrontation.