The richest Congressional district in the US is the so-called "silk-stocking" district of New York City's Upper East Side, with a per-capita income of $41,151 per year. The poorest Congressional district is a largely Hispanic-immigrant district in Los Angeles, with a per-capita income of $6,997 a year. In 1973 the poorest fifth of America's families had incomes that averaged $13,240 a year (in today's dollars); in 2000 the average incomes of the poorest fifth were the same: $13,320. By contrast, the richest 5% of America's families in 1973 had an average income of $149,150, and in 2000 the richest 5% had an average income of $254,840. The increase in inequality was large enough to give a 2/3 income boost to the well-off over a time when incomes in the middle grew by only 10% and incomes at the bottom not at all.
To outsiders, the most peculiar thing about America's rising inequality is that so few Americans object. Surely a society with a skewed income distribution is worse off than one in which incomes are more equal. An extra $10,000 a year does little to raise the well-being of a multi-millionaire, while a deficiency of $10,000 a year makes a huge impact on how a middle-class family lives.
If you follow Nobel Prize-winner James Buchanan's utilitarian principle that you should evaluate a society's social welfare by imagining that you have an equal chance of being poor and rich, it is easy to judge that the more equal society has a better set of social and economic arrangements. From there it is easy to make the leap to the position that - so long as redistributive taxes don't slow economic growth - when inequality rises, it is the government's duty to tax the rich and transfer money to the poor to offset the rise.
Yet there are no calls in mainstream politics to sharply increase the progressiveness of the income tax. Indeed, even at the left end of mainstream discourse, the boldest call is for the well-off merely to contribute their "fair share" to paying for the costs of government.