For a long time, I thought the A in STEAM stood for "and", as in Science, Technology, Engineering and Math. Silly me.
To explain my POV, I need to preface this with some definitions. There may be people who disagree with how I define these words but it's hard to have a conversation without a common understanding.
Science is the practice of organizing a system of verifiable facts through observation and repetition.
Technology is the collection of skills and processes derived from scientific knowledge.
Engineering is the application of scientific knowledge to intentionally effect an outcome typically through machine or structure.
Math is really just a subset of science, albeit a very abstract one (props to maddog175 for already
saying this).
Art is expression meant to tap into human emotion. Emotion happens in the observer's head. That is the antithesis of science. It seems incongruous to me to include it. That doesn't mean it's unimportant, but it is dissimilar to the others.
Human beings are complex creatures. Each of us is an emotional being. We all have some art that speaks to us. But we also all have the capacity to observe and draw rational conclusions. One is not inherently more important than the other but they are not the same thing.
The question we should be asking is not whether it should be STEM vs STEAM but what is the mission of FIRST? If it's to produce well-rounded individuals through robotics, go for STEAM. If it's to get more people to learn, love, and live science and its related disciplines, go for STEM.