This ignores that taxes are a thing that need enforcement. Its like saying basic necessities should be free, the world should be without pollution, or cancer shouldn't exist.
For taxes, I favor land value tax. Basic necessities can absolutely be free under it, as the super rich hold plenty of land. We can have a world without much pollution if we switch away from fossil fuels, and if we take the lifecycle of chemicals into account. Note that excesss carbon dioxide is pollution too. Regarding cancer, medical science is working toward it.
Assuming you are talking about free basic necessities: I can conceive it fine, I just also understand that conceiving doesn't mean it will work, and history has shown it won't. Me making the statement was itself conception no?
I can conceive of a million different economic systems, but I also understand most of them are infeasible, and the risk of running the experiment is extremely high, with little to gain in a my country, where obesity is a much larger problem than starving.
Define "pie in the sky", because you have described the utopia that every eco-socialist has been chasing for 100 years...
The problem that makes it infeasible isn't the math, or the technology, it's people. Communism would work beautifully... if everyone in the world was different.
A system where the population's wealth disparity keeps getting worse is nothing to be proud of. There have been systems of government in history where the system's total wealth made everyone more equal while preserving the reward for effort.