BOB HERBERT: As the Economic Policy Institute has reported, the richest 10 percent of Americans received an unconscionable 100 percent of the average income growth in the years 2000 to 2007, the most recent extended period of economic expansion. Americans behave as if this is somehow normal or acceptable. It shouldn’t be, and didn’t used to be. Through much of the post-World War II era, income distribution was far more equitable, with the top 10 percent of families accounting for just a third of average income growth, and the bottom 90 percent receiving two-thirds. That seems like ancient history now. […]