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You assume that economic production is as simple as discovering a baseline inventory to maintain, and then assigning production orders to maintain that inventory. Never mind the economic calculation problem, changes in technology, changes in supply and demand, or any other favtors in the real economy.

Lol, I don't care why you can't give your products away, but if you can't then you need to produce something else.
Food is always a good choice.
If we don't want to overcomplicate things much.

The facts are that as long as the people that keep the train on the track today, keep it on the track for tomorrow, it's not coming off the track until they stop doing the work, and even then, they can hand it off to somebody younger.

The world only needs so many shoes, that is a knowable number.

How many hours each person would need to give could be debated, especially in light of the changed paradigm, but this too is a knowable number.

All the 30% of us that work a job would need to do is to continue production.

Don't let the banksters fool you, they need us more than we need them, we already grow, harvest, distribute, cook, and clean up the food.
They have to pay people to do it.

Robots will not replace us undercrapitalism until starving workers are no longer a concern.
The reason they havent replaced us like they did spinning wheels and buggy whips is because the rich people are scared of the masses rising up in the crunch.

Sadly, they could consume for free, too, but prefer lording their game over us.

It's our buying into it that perpetuates it.