If your system needs absolute theoretical purity to work, then it's worthless. And that's true of both communism and free market.
It seems a bit like saying humans will never fly. It's a question of technology level, in the sense that governance is a form of economic technology. Which is what leaves it open to people saying it can be done better.
The best solution changes over time, essentially. It's a question of fitness to the current context.
And until you get a technology that prevents leadership to be egoistic and corrupt, Communism is never going to work.
I'm not holding my breath for any of those tech to happen.
[1]: interestingly enough, such a condition is pretty much antithetical to capitalism as it requires capital to be free.
Most successful economies are largely market-based, as things stand today. Even the successful command economies (i.e. China) use markets extensively.
Unless you mean perfectly free markets will never be perfect resource allocators. Well yes, perhaps, but what does that matter if there's no perfect solution? The nudges required to 'fix' markets are a form of technology, as discussed. As such, it either exists and is effective or not.
And even these economies are structured around monopolistic and oligopolistic actors.
They are as related to “free market” as northern European countries welfare state is related to Communism.
Like there's a whole zoo of healthcare provision approaches, for example. Single payer can work fine (ala Norway), but so can Bismarck (ala Switzerland). The latter is a technological architecture that _enables_ similar or better outcomes, while being closer to a fully market-based approach.
Also, if you call regulations “technologies” (which I don't disagree with) then “free market” means technology-free.
Also, I'm not sure a free market is technology-free per se. What you're talking about is specifically ancap-like, but most free market frameworks involve a state actor that should (among other things) not allow for itself to be weaponized against other market participants.
Like the paradox of tolerance, you can't tolerate a free market for bribing your way to benefit from the state's monopoly on violence. I don't think the existence of this paradox destroys the value of free markets or tolerance.
I'm sorry to tell you we don't build spaceports on top of mountain, for a reason.