Re: yeah but what about the jobs...?
Some form of economy would still exist, though. People would exchange value for value in some form or other, even if it's just uptwinkles on facetwat.
Ignoring the consideration of value is the failure of all central planning. The value I place on some old toys I still have hanging around is immense. Some people wouldn't pay pennies for them. Someone else might value them enough to offer me a lot of money (or something else that I value), which I might consider a worthwhile exchange.
That's all an economy is, in the end. Exchange of value for value. Money is simply one means of measuring value but it is not the only means of measuring it. In a post-scarcity society we may not need a medium of exchange for commodities that can be manufactured on demand, but there will still be items that are valued by people and they will still want to exchange other things of value for them. A painting by a great artist. He may give it away for free. He might not. He could be induced to part with it for something of sufficient value. Or someone helps their friend move a couch around their living room, and in exchange they get a few beers. Exchange of value for value. That's an economy in action.
The claim that the notion of economy would be absurd in some far-off post-scarcity society is itself absurd, because it ignores that central element of what forms an economy in the first place. Forget "utility" and grand theories of things. Economies form from the bottom up, through transactions between entities. They emerge from the value those entities place on things.
That's why central planning fails in the end. It has no notion of value outside of what the planners consider to have value, and what they consider to have value has no relation to what you or I or anyone else considers to have value.