To be successful in a professional environment, you have to be able to manage your emotions. If workers didn't have some level of emotional self-control, meetings would regularly devolve into shouting matches and teamwork would break down, grinding productivity to a halt.
However, there's also a lot to be said for authenticity at work. If you're constantly forced to plaster on a smile, while you seethe away underneath, eventually it will take a toll on your life and career. Faking happiness at work can cost you.
Consider the science: