I’m not saying it will contract the economy or create fewer opportunities. That’s you staying in a box. Technically speaking in a world where we only need the labor of 10 to 25% of the populace to provide for the basic needs of the populace provide MASSIVE opportunities. Just not for old world style “jobs”. People now have the opportunity to create. Art, science, whatever they feel like. And as for the economy if we get anything close to replicators the economy quite simple doesn’t matter anymore.
It’s a very small number of people needed to design these machines. They, like so much else we have, would be built by other machines. And thanks to the web things already basically sell themselves. The supply chain is much smaller and simpler. Our current economy is built on harvesting raw material, delivering it to somebody that will turn it into a middle product, deliver that to somebody that will turn it into a finished product, then deliver that to the seller. A 3D printer based economy will turn raw material (a much cheaper, easier to get, less labor intensive, probably recycled raw material) turn it into print media and deliver it to our homes. 2/3 of the process (and all the jobs that it includes) just evaporated.
If these technologies continue on the path they look like they’re on we will need to change our basic concept of the relationship between people and stuff and how the former acquire the later. Jobs will quite simple not be necessary or available for most of the population, and yet people without jobs will not be leaches or poor, they will be normal. The big question is does it turn out well like Star Trek or bad like Judge Dredd.
Your scenario is based on conjecture and sides with negativity and fear of the future in which there are no guarantees except the promise of freedom and the free market economy, which is freedom in action. I'm in the better company of historical fact and economic theory that embraces the freedom. I don't understand people who call themselves "conservatives" who would rather have "guaranteed" results (a socialist illusion if there ever was one) than embrace the risks and rewards of freedom and the free market economy.
Historical fact clearly shows that socialist government guarantees results but doesn't deliver (many ancient and recent examples of that). It also shows that freedom and the free market doesn't guarantee results, only opportunities, requires faith, risk, and bravery, and has always resulted in a happier society but also a more prosperous society. Your world, one that fears freedom, would have socialist governmental guarantees (the only other alternative to freedom and the free market), and the historical record of socialism is poverty and misery.
Think I'll go with fact, sound theory going all the way back to Adam Smith, and a very good track record.