I have mixed feelings about this. Why is anger an appropriate response to sin? On the one hand, because to sin is to go against God. But in getting angry, we also go against Him. We should approach the sinner in love and try to correct the behavior gently, instead of acting in anger. And yet, sin cannot be tolerated because it is an affront to God, and to let it go unchecked is to let it continue to fester and grow.
Capricious or uncontrolled anger is like throwing gasoline on a fire that's already out of control. Someone stands a great chance of being permanently hurt. Could be an innocent bystander. Anger that brings about justice can be repentance, or it can be some form of fair punishment to the guilty. It is not a knee-jerk reaction done out of emotion, though.