They were going to fire up the LHC to open a dimension, which can only happen when the moon is casting a shadow 6000 km away. Then aliens... or something.
Real everyone-eats-ice-cream-and-dances-all-day hasn't been tried either. Just because you describe a set of circumstances doesn't mean those circumstances can exist, and it especially doesn't mean they can be stable long term.
Scarcity is a fact of nature. You cannot rationally distribute scarce things without knowing people's preferences, so you either need to continuously solve the economic knowledge problem (which requires a huge state apparatus, which will be taken over by a dictator), or a means of exchanging goods between people to better suit their preferences (at which point you have invented capitalism).