...machines don't buy anything and if nobody buys anything, nothing gets made and people die of hunger. We simply need work, if only to establish a personal value that we can use as a means of trade for the things that we require and cannot provide for ourselves.
What people need is the intelligence and imagination to enjoy their free time without the need to spend money they don't have.
There are only two fundamental limiting factors on the future prosperity of mankind. They are, energy supplies and imagination.
Energy supplies are extremely abundant. I can't see any problem there. As an example of just one abundant source of energy; if one were to cover the largely uninhabited areas of the Sahara Desert (about 9 million square kilometres) with modern Solar Voltaic Panels, the amount of electricity generated would be about 20-30 times the current world-wide consumption of energy, converting all types of energy to kilowatt hours.
There are many deserts around the world which are just waste lands, serving no useful purpose, not to mention the millions of square kilometres of building-roofs and walls exposed to the sun.
Some folks seem worried about world food supplies. They believe that, with a rising world population, the planet might not be able to produce the amount of food required to adequately feed everyone.
Nothing could be further from the truth. The amount of food wasted worldwide, not eaten because the serving was too much, thrown away because it passed its use-by date, discarded during processing because only the refined tasty bits were required, inadequately stored due to lack of refrigeration, and not transported to markets where it's needed due to inadequate road systems, currently amounts to about 1.3 billion tonnes per annum. (That is, 1,300 million tonnes per annum).
In other words, the amount of food wasted is more
than enough to feed all the world's hungry. In addition, the amount of food overeaten by all the overweight and obese people in developed countries would also be enough to feed more
than another billion future population.
Some people believe there might be a shortage of water that would put a limit on agricultural production and that future wars might be fought over such shortage.
Wars are fought for all sorts of unjustifiable reasons, but there's definitely no shortage of water. It falls freely from the sky, and the seas around the world contain huge quantities of it.
What there may be a shortage of is imagination to devise ways of transporting water from where it's plentiful to where it's not, and recycling and purifying water to drinking standards. The technology and the energy supplies exist to solve all these problems. If they remain a problem, it's due only to incompetence in dealing with the obstacles.