I have previously asserted that a truly free market produces an outcome that resembles communism. This conclusion follows from an investigation into how free markets behave, but the connection between free markets and communism can be made more explicit.
A truly free market is a market free of all human coercion, active and passive. Active coercion refers to "gun to the head" coercion: the threat to actually cause suffering or physical harm to another. Passive coercion refers to the "let them starve" coercion, the threat to allow suffering physical harm to come to another.
Passive coercion is still coercion. Every ordinary human being will naturally act to avoid or ameliorate her own suffering or physical harm. To make passive coercion effective, the natural tendency to for a person to ameliorate her own suffering must be actively thwarted by the threat of active coercion. For the passive threat "work [for me] or starve" to be effective, I must also employ active coercion: "try to feed yourself, and I will shoot you."
While it is in some sense physically possible to have a truly free market in reality, such an arrangement is at best only meta-stable and requires continuous teleological adjustment. In 21st century terrestrial society, we must view a truly free market as a purely theoretical construct. Still, even as a theoretical construct, the notion has some value, precisely because of the independent value ordinary people place on freedom in general.
A truly free market is efficient, but efficiency is an equivocal term. Efficiency is some output value divided by some input value, but we must specify less ambiguously what output and input values apply to construct a coherent notion of the efficiency of any process. A bus, for example, is less efficient than an automobile in terms of vehicle miles per gallon of fuel, but it is more efficient in terms of passenger miles per gallon. On the other hand, a bus is less efficient in terms of passenger time per miles traveled.
Efficiency can also have a positive or negative sense, i.e. the "best" system might either be the maximal or minimal value of some ratio. For example, we can talk about about the efficiency of an engine in terms of heat produced divided by fuel consumed: An engine is more efficient to the extent that it minimizes this ratio. Any positive or negative construction of efficiency can, in theory, be transformed into an equation of the opposite sense; in practice, however, it is often the case that one sense is much easier to measure than another. A more heat-efficient engine (negative efficiency) will translate into a more mileage-efficient engine (positive efficiency), but an engineer can easily directly measure the heat-efficiency of an engine without having it travel any miles at all.
It is often supposed that a truly free market is efficient in terms of value produced per cost of production. But this sense of efficiency is not supported, precisely because it is too difficult to measure the actual value (the use value in Marxist terms) of what is produced.
A free market is efficient at setting the exchange value (price) of a commodity to its opportunity-adjusted cost. A free market does not reward the production of commodities of higher use value, regardless of how well we are able to define use value. A free market rewards the identification and exploitation of bottlenecks, i.e. imbalances in supply and demand. But the very nature of the truly free market embodies a negative feedback process: the narrower the bottleneck (the greater the discrepancy between supply and demand), the more that bottleneck attracts additional labor, thus raising the opportunity-adjusted cost of the commodity, until the price and the cost are again in equilibrium.
In a truly free market, then, any excess value (the difference between the use value and the exchange value) accrues to the consumer of a commodity; the consumer is responsible only for replacing the opportunity-adjusted cost of the commodity.
We can correlate this outcome precisely to the canonical (if poorly stated) slogan of communism.
From each according to his ability. Each person is responsible for replacing by productive activities the opportunity-adjusted cost of the commodities she consumes. To each according to his need. Each person receives the full (subjectively-defined) excess value of the commodities she consumes.
Therefore a truly free market is inherently communist.