The other day, a newspaper writer joined the chorus of angry voices about the bad effects of new technology. “There can be no rational doubt that [it] has caused vast injury.” It is “superficial, sudden, unsifted, too fast for the truth.” The day was in 1858, and the quote was about the telegraph. Similarly, the telephone, radio and television have each in turn been seen as a source of doom.

Mobile devices like smartphones are just the latest example. Parents fear that they will make teenagers more socially alienated and...