> Why can't there be people interested in self-driving cars or social networks for their own sake?
If you are interested in self-driving cars, but you are not interested in the effects that self-driving cars have on society, you are not actually interested in self-driving cars: you are interested in yourself. To be interested only in the problem-solving aspect of a domain is, first and foremost, to be interested in your own mastery. I am not saying that it is bad to be motivated by mastery: I am personally very motivated by mastery. It's what has kept my interest after a decade of programming professionally. I relate to being interested in a problem because it's an interesting puzzle.
But we should not pretend that being interested in the aspect of solving a problem is the most genuine manner of interacting with that problem (or the opposite: that caring about the side-effects of your work more than you care about the work itself is somehow lacking in earnesty). It is not. What you are building does not stop at the problem-solving phase. How the things you build affect the world is what you have done. If we set our ethical standard at "so long as I am interested in doing the building, I am being earnest", our efforts will forever be deployed by others, perhaps with effects that do not align with our values.