Perhaps it's become harder in our current society, but many great projects of man were economic folly.
To give one admittedly a little cliche example, landing on the moon never made any economic sense.
This is a statement of reality, not economic system. A society that decided to divert resources, today, to building a Dyson sphere on Alpha Centauri would fail, irrespective of economic system, because the goal demands more resources than it can sustainably divert.
Yes, that's my point. The worry about "economically feasible" in the ancestor comment is a question of what plans are realistic with unlimited motivation. It's not about economic systems holding us back.