In 23 Things They Don't Tell You About Capitalism Chang explains why it is not true that businesses should be run exclusively in the interests of shareholders. In a nutshell stockholders interests are not necessarily aligned with the long term interest of a company. A stockholder can shift his money very quickly. So if a company can maximize profits today, by reducing wages or resisting investment in equipment, that can translate to big payoffs for a stock holder today. They can reap large dividends. And if that means down the road the company is not capable any more, that's OK because it's easy to jump out. There's risk here for the stock holder because he may not get out in time, but if he's smart he can do well.
That's not true of a worker. A worker can't just learn new skills or move to a new location in a single day. So a worker is more interested in the long term prospects of the company that he works for.
Chang uses GM as an example. Decades ago GM was on top of the automotive world. To please Wall St they focused less on innovation and investment in themselves and more on paying out dividends. They rode that strategy all the way to bankruptcy and state bail out. The stock holders were happy and didn't really mind the exorbitant CEO salaries. They were paid well. But the workers had tough times.
Steven Colbert kind of illustrates the point in this commentary related to Romney. It touches on the idea that what we need in Washington is people with business experience.