Last week Alan Krueger, chairman of the president’s Council of Economic Advisers, gave an important speech about income inequality, presenting a relationship he dubbed the “Great Gatsby Curve.” Highly unequal countries, he showed, have low mobility: the more unequal a society is, the greater the extent to which an individual’s economic status is determined by his or her parents’ status. And as Mr. Krueger pointed out, this relationship suggests that America in the year 2035 will have even less mobility than it has now, that it will be a place in which the economic prospects of children largely reflect the class into which they were born.

That is not a development we should meekly accept.

Mitt Romney says that we should discuss income inequality, if at all, only in “quiet rooms.” There was a time when people said the same thing about racial inequality. Luckily, however, there were people like Martin Luther King who refused to stay quiet. And we should follow their example today. For the fact is that rising inequality threatens to make America a different and worse place — and we need to reverse that trend to preserve both our values and our dreams.