Is This a Zero Sum World?

Many people assume that there's a relatively fixed amount of wealth and if one person becomes a billionaire, it can only have happened at the expense of other people. I think what you're pointing out or putting your finger on is that, well, when wealth is flowing, it doesn't usually stop in one place, it goes in various places. So why should we be worried about the fact that in the United States you have such a wide disparity of wealth?