Except for where there can. Economic productivity is nowhere close to decoupling from population mass yet, but when it does, you won't need low or semi-skilled workers.
There is a careful calculus happening at every level comparing the productivity of a human versus machines (and other humans). To deny that competitive spirit, à la Greece or Italia, builds systematic inefficiencies into the economy.
At a certain point there won't be a place in the world for unskilled humans - they will be un-differentiable from a defective tool.
TL;DR This may be a problem, but will be un-avoidable. Social structures, demographics, or both will have to adapt to new realities of productivity.
The paper concludes that in the short-run, rising productivity decreases inflation, increases the current account balance, increases GDP, and increases unemployment (and real wages) as aggregate supply increases without a commensurate increase in aggregate demand. The system starts equilibrating as people internalise the higher productivity into their investment assumptions.
We could see falling rates on student loans coupled with rising returns on education (note: not just college education, as the OP pointed out) as increasing the incentive to invest in one's education. Given that our culture creates barriers to education the older one gets it seems like we will have a wasted generation of un-skilled workers who will just need to be worked through the system (being a cold, pragmatic macroeconomist here). Being civil to those people without incurring undue cost to the system will be the challenge.
[1] http://www.treasury.gov.au/documents/239/PDF/paper07.pdf
You don't need workers to have productivity, but you need people not being rich to have riches. And those people need to be fed, clothed, etc. And they also need money, to be able to buy things and services, else you cannot sell them.
So, you either turn into a Star Trek/socialism scheme, where social wealth is shared, and rich men are those that take more share by power alone --like kings of time old--, or you have a problem or keeping people occupied.
If you define rich to mean "I have way more than I will ever need" then there is ultimately no reason that everyone can't be rich. It just takes a while to get there.
Personally I'd prefer the latter. Eliminating poverty makes everyone better off.
The problem I described is multi-faceted, and I might not have made a good job at it, or some people might not have understood me (judging from the knee-jerk downvotes).
One issue is societal wealth. As a society, everybody can be "rich" in the sense you describe, but I already addressed that in the part where I write about the "Star Trek/socialism scheme, where social wealth is shared". I am fine with that kind of a society. I just don't see that this is what we are currently approaching with automation, etc, but rather huge poor masses and an middle class in decline.
So, my other argument was about what is actually happening, i.e. the continuation of the current model + automation. And what I said, is that if you believe --as many do--, that corporations, enterpreneurs, buying and selling stuff, in essence a market economy is crucial, then you need poorer people with jobs, ie. you need consumers. You cannot have a market economy AND everyone being rich in the "I have more than you" sense, and you cannot have a market economy AND the great masses out of work due to automation.
So, my argument is, automation is ultimately non compatible with a market economy. You get either sharing for everybody (i.e no market economy), or a collapse in buying power / sales (i.e a poor market economy).
(A final point, re everyone being rich in the "I have enough" sense: beyond the basics, "needs" are themselves a social construct. To a caveman, or a 17th century peasant, a man working at McDonalds with a house, tv, food, internet, bathroom, modern medicine, etc, seems as "more that he will ever need". To his contemporaries, not so much).
You need people not being rich to have riches
Echoing another point made in this thread, but wealth differentials doesn't mean you need to have poor people. The least well off person in a society may not have everything they want - most people don't and probably should not, if we want aspiration and ambition to have a place in the future - but they'll have their basic human rights fulfilled (a roster that gains mass with economic development).
The "material and energy intensity of consumption, per capita, has increased exponentially over the past centuries" EXACTLY because of the creation first and constant availability of "an army of low-wage consumers".
People were taught to hold jobs in the way we do now, and they were taught to consume, in the way we do now. The vast masses of the people not only consumed much less, but made their own everything, from clothes and shoes, to vegetables and housing. Like an Amish community.
A decline in the middle class, e.g by migration of their jobs abroad, translate to a decline in economy, unless you can create new jobs at the same rate, which currently we can't, and the economy took a hit.
Echoing another point made in this thread, but wealth differentials doesn't mean you need to have poor people.
No, but a market economy needs people poor enough to have to work and at the same time rich enough to be able to spend money on things.
Automation can eliminate the need to have people working, but it cannot eliminate the need to have people spending --except if you move beyond a market economy.
