I think what this person isn't getting is the feeling of anger and the actions one takes in response to feeling anger are very different things. Feeling anger is part of being human. Acting angry is absolutely called for in some circumstances, but it can easily spin out of control and infect other parts of your life that have nothing to do with what you're angry about. Dollars to donuts this person has let anger infect their life to the point it's disrupting something, like maybe their relationships or employment, which is why they're in therapy.