Almost a year ago, hundreds of thousands of immigrant workers and their families slipped out from the shadows of American life and walked boldly in daylight through Los Angeles, Washington, Chicago, New York and other cities. “We Are America,” their banners cried. The crowds, determined but peaceful, swelled into an immense sea. The nation was momentarily stunned. A lot has happened since then. The country has summoned great energy to confront the immigration problem, but most of it has been misplaced, crudely and unevenly applied. It seeks not to solve the conundrum of a broken immigration system, but to subdue,...