Anger leads to evil.

 Refrain from anger, and forsake wrath! Fret not yourself; it tends only to evil. For the evildoers shall be cut off, but those who wait for the Lord shall inherit the land.

Psalm 37:8-9 (ESV)
 
Being angry is best left to those who are perfect and can use their anger to benefit those with whom they are angry. My anger does not achieve much good. It makes me tense, causes grief, and makes many not want to be around me. Often, it is motivated by my self-centered worldview, and aimed at those who do not acknowledge that the world revolves around me (at least my world).
 
James tells us that man's anger does not produce God's righteousness. It produces many words that one regrets uttering, many gestures one regrets giving, and many situations in which one regrets being placed.
 
Anger leads to evil, and evil doers are cut off from the life that God has for them now and in eternity. Anger is the fruit of the tree of self-centeredness, and it needs to be dealt with swiftly before the generation consumes its fruit to come.