If we're talking shorter scale, people have traditionally hand-waived it with 'Oh, these jobs will go away, but they'll be replaced with other, higher-skilled jobs!'.
That's an economist's idealism and doesn't fit reality.
For a while every economic advance seemed to mean more and better jobs for horses. But then the automobile comes along and there's no more need for horses and we can see what happens to an animal that has no economic reason to exist.
We still have a much smaller number of horses for the few economically viable roles a horse can fill and as toys for the wealthy.
The question is if labor will follow the same path.
In other words, I have no idea where all the white collar workers are supposed to go.
Yes, but those were horses. Now substitute the word 'human'.
But yeah, the robot armies don't need grain so why hike up the price of bread? Lack of grain makes those people resentful which means you need to deal with their anger. Sure, it can be dealt with but it's just cheaper to give the humans grain so they are docile. This is basic governance 101 that goes back to the romans (and further).
They also didn't slaughter all horses immediately. You can't eat that much horse meat anyways. It happened piece by piece.
The only good reason for an abrupt mass culling of the 99% (for a coldly calculating rich person with no empathy) would be game theory, i.e. them not being a contender for power any more. If there are no humans, there is nobody who can question the control of the 1%. It would be thus less about economics and more about power.
I am really rooting for the bottom 99%, myself being a part of it, but I really don't know what will happen to us.
