An obvious example is nuclear weapons. Amazing science, incredible engineering, awe-inspiring power. But I doubt you would make the same critiques of people who were anxious about the world they create. A world in which MAD exists is fundamentally different than one where it doesn’t.
Regarding your grandfather, it’s a pretty well-supported hypothesis that younger generations are less happy and more depressed because of technology from the very industry pushing AI onto them! Why should you expect them to be excited about a new world-changing tool from the same set of companies that brought them an infinite doom-scrolling feed of self-doubt, the increased polarization of politics, the viral spread of conspiracy theories, and a higher rate of youth and teen suicide than ever before?
Technology isn’t fundamentally good or bad, but it can have very negative impacts on society. It seems like people are catching on to that fact.