The have-nots of today might as well be kings to those living 1000 years ago. Still, having a strong middle class is good for everyone, regardless of moral imperatives to help others.

Why is that? Even if there was enough wealth around to make everyone a king by today's standards, if someone had no marketable skills or capital, why would anyone give anything to him? It would be up to the haves whether they wanted to play Mr Nice Guy or not, and I don't think the choice is obvious.

Everyone in the middle class is a king by the standards of the 1950s. I have, as a starving student, more wealth than any emperor of Rome. The assumption that we're not already upstream in the singularity is just bias of perspective

Presumably you have a job, or you have parents with a job that are supporting you, or you live on student loans given to you by people who expect that you will get a job and pay you back with interest. If there's a hypothetical machine that can do your job, then you won't get one, and there's no reason other than charity for anyone to give you money.

Until now, if a machine took a job, that just meant that another worker was available for another job that a machine couldn't do. Machines are pretty dumb, so that's not hard to find. A kid with Down's syndrome can sweep the floor at Taco Bell, but a machine can't. That changes with the singularity.