American plutonomy

Maybe the most persuasive argument against America's growing wealth disparity is not a moral one, but a practical one: extreme wealth disparity doesn't work well because concentrating spending power in the hands of a few is a recipe for economic turmoil.  Michael Lund thinks so: 

[H]istory makes it clear that when economies mutate into plutonomies they become dangerously volatile. Just as a ship with a broad base is more stable than a top-heavy boat, so an economy in which well-paid workers create mass consumer markets for the goods and services they provide is more stable than a top-heavy plutonomy.