Other factors that may be at play include an increasingly high-tech economy, which has put a premium on skills and education. Also, whether because of market forces or the policy climate, a rising share of national income has been going to corporations (as profits), while the portion that goes to pay workers has declined. That shift benefits owners of corporate stock.
So long as a boom time kept most people's financial fortunes on the rise, few jumped up and down over the greater concentration of wealth in fewer hands. But the hard times that ensued after the financial system's near-collapse in 2008 have changed that. It's much more top of mind now that the share of people officially deemed to be living in poverty has jumped from about 12.5 percent to 15 percent since 2007, wages are barely rising for the middle class, and many millions more people are out of work.
America has seen the income gap widen before. Often, when class differences moved to center stage, the result has been a political realignment that tilted power and policy at least modestly away from the rich and big business. The 1930s and, before that, the Progressive Era in the early 1900s are prime examples.
But for every individual who is wringing his or her hands over income inequality, there's someone who sees it as the American way.
"You'll make money according to what you've done in life," and according to your education and skills, says Paula Alibrandi, who works as an executive assistant in Boston. "That's only right."
Here's a look at the key arguments:
It's bad for the economy
Nick Hanauer isn't the person you'd expect to be vocal in the fight against inequality. He does venture capital deals as a founder of the firm Second Avenue Partners in Seattle. He's part of that top 1 percent, not one of the so-called 99 percenters involved in various "Occupy" protests in recent months.