A man of wrath stirs up strife, and one given to anger causes much transgression.
Proverbs 29:22 ESV

"Blessed are the peacemakers". A consistently calm demeaner will help other people remain calm and willing to talk out disagreements. However, anger is like fire. One angry person can nullify the positive effect of 10 peaceful people. He is quick to take offense and to cause offense, which makes other people angry, and so on.