Inequality is inevitable; life is a bell curve. Such are the brute facts of biology, which can only evolve because some living things are better at reproducing than others. But not all inequality is created equal. In recent years, it’s become clear that many kinds of wealth disparity are perfectly acceptable — capitalism could not exist otherwise — while alternate forms make us unhappy and angry.

The bad news is that American society seems to be developing the wrong kind of inequality. There is, for instance, this recent study published in Psychological Science, which found that, since the...