The beliefs about replicators and transforming planets like mars are just a futurist fantasy about how our problems will all be magically solved in the wonderful future, its great escapism to avoid caring about real issues we really can solve right now, and a very convenient dismissal if issues we can address
right now with "The future will fix it"!.
Note, many of the people that don't need to work are extraordinarily wealthy, hundreds of thousands of times over what would be required to lead a reasonable life, their wealth bases usually built, directly or indirectly, from the efforts of the same people that have to work until they are 70.
But yeah, in the future, somehow this arrangement will change into a magical utopia, not a situation where those same wealthy horde an even more absurd amount of power, while everyone else struggles to scrape by, or is just discarded entirely in the face of cheaper and better automation that is owned by the wealthier rentier class.
You see this callous disregard on HN every time an article about Uber or Amazon treating their employees like shit, remarks to the effect of "they shouldn't be complaining, cant wait till they are replaced by robots", and I think its disgusting, but its a telling remark about how employees are going to be viewed increasingly in the future.
If we don't even want to bother broaching the serious wide-cutting issues we have right now with poverty and inequality in our society, I fail to see how the hell technology that effectively massively magnifies the economic power of whoever can afford them the most will do anything but make the situation far, far more dire.