[jbooth]

The middle 50% or so of the income scale, whatever that happens to be? Pulling that out of my hat.

The study you linked upthread said a bunch about income mobility or lack thereof. I see that as a much bigger problem than equality for it's own sake, although I'd be very concerned about a completely hollowed out system.

[yummyfajitas]

With that definition, there can never be a "lack of middle class jobs" (to borrow your phrasing). Precisely 50% of the country will be middle class at all times.

[jbooth]

Yeah but there can be a transition of those jobs from "paying a wage you can support a family on" to "not doing that". That seems to be what's happened, we've replaced a lot of trade skill jobs in manufacturing, etc, with non-skill jobs at Walmart or the gas station.