I would say people shout in an argument to satisfy thier own ego. People shout in an argument to put the other person down. How do you feel when you shout at someone really bad and they cant say anything back? You feel this weird happiness inside of you. I think its the happiness of beating the other person, the happiness of thinking you're superior, the happiness of satisfying your ego. I dont even think shouting is going to lead us to a conclusion, only temporary silence. Im not that much of a shouter by nature, if someone shouts at me, ill listen to the bs. The faster it gets over, the better it is.