The stock market turmoil unleashed by the artificial-intelligence industry reflects two fears that are increasingly at odds.  One is that AI is poised to disrupt entire segments of the economy so dramatically that investors are dumping the stocks of any company seen at the slightest risk of being displaced by the technology.  The other is a deep skepticism that the hundreds of billions of dollars that tech giants like Amazon.com Inc., Meta Platforms Inc., Microsoft Corp. and Alphabet Inc. are pouring into AI every year will deliver big payoffs anytime soon.  The dueling anxieties have been brewing for months. But they’ve shifted to the...