Three weeks ago, Apple Inc. chief Tim Cookripped into technology companies that “carefully assembled, synthesized, traded, and sold” then “weaponized” their users’ data. “These stockpiles of personal data serve only to enrich the companies that collect them,” he told a receptive audience in Brussels.

If executives at his unnamed targets—Facebook Inc. and Google parent Alphabet Inc.—rolled their eyes, you can understand why. Mr. Cook is, after all, talking his book: Apple makes its money by charging premium prices for its products....