The advocacy documentary “Inequality for All,” featuring former Clinton administration Secretary of Labor Robert Reich, aims to be economic policy’s “An Inconvenient Truth,” a left-leaning wakeup call for most Americans (affluent or not, young or old, Republican or Democrat) who have no idea just how hyper-concentrated our nation’s wealth distribution actually is.

The difference is that unlike Al Gore, Reich has an engaging sense of humor.

It’s a relief to see important issues being discussed rather than shouted about. The film is structured in parallel with a semester in the Wealth and Poverty course Reich teaches at UC Berkeley. “Some inequality is inevitable if people are going to have the proper incentives to be productive, work hard, be inventive,” Reich says.

Problems arise when the income disparities become too acute. Today the 400 richest Americans have more wealth than half the country’s population combined. “When the middle class doesn’t share the gains, you get into a downward vicious cycle” of falling consumption, company downsizing, falling tax revenues, government program cuts, less educated workers and rising unemployment.

Directed in workmanlike fashion by Jacob Kornbluth, the film makes its case about the hollowing out of the middle class with a refreshing lack of academic jargon. It flows smoothly across talking points, graphs and interviews with people enjoying the largest share of the pie and those subsisting on crumbs. Alongside clips of clashes between police and strikers during Hormel’s P-9 strike, we learn that a meatpacker in the mid-1970s made $41,000 a year adjusted for inflation, vs. $24,000 now.

The film’s talking heads say surprising things. Take wealthy Seattle entrepreneur Nick Hanauer, whose large down pillow plant has plenty of employees. He argues that the deification of business owners as “job creators” is mere PR. The real job creators are the everyday consumers who power 70 percent of the nation’s economic activity. When the customers’ wages and wealth dwindle as the rich get richer, “business is tough because fewer and fewer people can afford to buy the product.”

The film notes that the nations that have fared best in the new globalized, high-tech world are those that have invested in creating a well-educated workforce. It’s not so much workers’ wages that determine a company’s profitability but the value they add.

Reich ends on a note of realistic optimism. He frets that he was not effective in shaping policy while in Washington, which is designed to respond eagerly to deep-pocketed donors but not so attuned to the needs of Joe and Jane Voter. Nonetheless, Reich gives his students an inspirational pep talk on the last day of class. “If anyone feels cynical about possibility of social progress,” he says, “just consider where we have been.”