Because human anger does not produce the righteousness that God desires. James 1:20
I have a dear friend who used to tell me to "blow it off" meaning basically to let something go. When you are agitated about something if you do not learn to release your anger, it can explode and become much worse. That is probably what we see on our nightly news when an angry person or crowd just could not and did not 'turn the other cheek' thus boiling over into confrontation and violence.
Anger does not produce anything good. It destroys relationships, breaks things, hurts, and glorifies the enemy Satan. Sure people are going to be upset at times but it is how you deal with it that matters. Don't allow anger to send you over the edge.
Ask God to help you maintain peace and joy when you really don't feel like it. You can master the anger monster.
PRAYER: Lord I love the feeling of peacefulness and do not like conflict. Give me strength when agitated to deal with it in a Christlike manner. In Jesus' name. Amen.