Humans need something to do. In times immemorial, something to do entails running around the savanna looking for edible scraps, collecting them, bringing them home and raising the next generation to repeat the process. A perfect machine that produces and delivers edible scraps with zero human effort required leaves actual humans with nothing to do. Having nothing to do is spiritually unsustainable. There is so much leisure or travel. There is so much make-believe work. After a while though, people will need something meaningful to do, something that undeniably pushes the inexorable wall of unbeing a bit further.

This is exacerbated by social effects. We confer value to other people by their ability to provide meaningful work. Assuming a perfect machine that does all the meaningful work, there is zero reason to confer value to any other human being. This is a recipe for disaster, and will hit us much sooner than the angst of nothing to do.