It's morally wrong to cause harm to another person.
Bob is insulted by a man on the street who calls him all sorts of bad names.
Bob wants to react to the man who insulted him.
Bob tries to reason with the man, telling him it's not necessary to be so spiteful.
Bob punches the man in the face with all his strength and runs away.
The man who insulted Bob realizes that they are in the wrong and makes an effort to improve their behavior.
The man who insulted Bob is badly hurt and needs to get stitches.