Maybe this has been answered already
It has, but I'll answer anyway
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who will be forced to build and maintain the automation machines
Nobody. Just as nobody is forced to write on wikipedia, create material in creative commons, start the Open Source Architecture nexwork, Open Source Ecology, build The RepRap, write Linux or take part in any other thousands of FOSS successful projects.
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and who will do the forcing?
Consequently, nobody.
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Also, who will decide how much each person needs, and what will prevent them from deciding they need more than others?
In order: the planet (resources available), scientific method, education, education, education. No forcing, no coercion, no baseless opinions, no bullshit.