The problem with stoics is they don't have an understanding of why emotions exist. So, let's pose that question: why do emotions exist? Looking at it from an evolutionary perspective, were emotions harmful to an organism, then the human race, over thousands of years, would have evolved to feel fewer emotions. Yet humans remain the most emotional creature on the planet (to our knowledge). Therefore, it stands to reason that emotions have allowed the human species to thrive in some way.
Emotions are what drive us to act, to make both the greatest and most horrible achievements in human history, from the lightbulb to the atom bomb. Take away emotions, and humans become little more than statues.
And if you need further convincing, look at Ned Stark. He lived as a stoic and died by the orders of the most emotional person in Westeros: Joffrey Baratheon.
Oh, and spoiler alert (and if that's a spoiler, then you need to watch GoT NOW).
I don't think it's fair to say that emotions have allowed the human species to thrive, due to some kind of evolutionary benefit. Just because emotions exist does not necessitate that they have been adaptive. Personally, I believe that emotions don't have significant adaptive or maladaptive value, which is a valid possibility considering emotions' continued existence. If there's no adaptive pressure to get rid of something, then it stands to reason that the trait is either adaptive or neutral. We shouldn't ignore the other possibility. We also shouldn't assume that persistent existence -> adaptive value. That doesn't seem reasonable. For example, our pinky toes exist. But I wouldn't consider that they have allowed the human species to thrive in any significant way, especially since Dr. Anne Holly Johnson, an instructor in orthopaedic surgery at Harvard claims that the absence of the pinky toe does not hinder us from doing everything we want to.
I actually don't believe that emotions exist with any kind of purpose. They're just reactions that are based in some kind of cognitive function. For example, anger and excitement probably involve adrenaline. Sadness and other emotions probably involve high or low levels of some other hormone or neurotransmitter. However, this is something that is common to most vertebrates, if not most mammals. Humans express and perceive emotions due to our intelligence, but the biological underpinning of emotions isn't unique to us at all. So I don't think humans are the most emotional creature on the planet so much that we are the most intelligent and able to communicate in the most complex or abstract manner.
Also, Ned Stark wasn't a stoic inasmuch as he was a person who operated with a strict worldview considering honour, which unfortunately, most others in Westeros don't ascribe to. He wasn't particularly emotional, but his downfall was not due to his lack of emotion but his unwillingness to betray those he believed were the rightful authorities. Also because he was captured and beheaded by force. If the most powerful man in Westeros has you in his grasp, emotional or not, you're screwed.