Have you heard of recessions in planned economies? Neither did I. There might be inefficiencies due to transaction costs, but not recessions.
The reason is that recession can be thought of as the way some capitalists hedging against uncertainty associated with the behavior of other capitalists - they cut labor costs when they are not sure if other capitalists are forthcoming with they orders. Stated differently, they try to externalize expected losses and shift it on labor - which of course undercuts their long term viability, but gives them a clear short term advantage.
Integrated systems or hierarchies (as Williamson calls them) avoid that uncertainty and associated transaction costs, so they are in a better position to hedge themselves against market fluctuations. Due to the economies of the large they are even able to absorb losses that small guys cannot.
Now, think of the planned economy as a corporation writ large. This economy-size corporation can hedge itself against market fluctuations, reduce some of market-related transaction costs - but it also operates in an environment where externalizing losses makes no sense, because corporation = the economy. Therefore, shifting losses on labor is like shifting those costs to another department of the same corporation, assuming that the state (which is the corporation) has to take care of unemployed workers.
Stated differently, recession is an effect of the free ride by small scale capitalists who attempt to protect their profits by shifting anticipated losses on others - labor and society at large. It is a rational behavior, given the circumstances. So it is intrinsic to the market system populated by small time operators.
The problem can be avoided only when hedging against expected losses by shifting them on others will no longer make sense. State ownership and central planning was one was one way of solving the issue - but it turned out to introduce unexpected transaction costs due to imperfect information and human greed. The Keynesian system is goes in the same direction by introducing positive feedbacks i.e. government temporarily absorbs the losses resulting from capitalist hedging against expected losses, and then "recoups" those losses from higher taxes during a boom.
Of course the system is not recession-proof, but it is much more stable than a system of small guys under a free market system. Two main reasons are that large corporations can better insulate themselves against market uncertainty than little guys, and that the small number of players significantly reduces the transaction costs of Keynesian policies.
To reiterate - small guys under free market = uncertainty, high transaction costs, free riding, instability, and the shortage of capital investment (which btw is the major problem of microenterprises). Big corporations and planned economies (Keynesianism is a form of a planned economy) effectively alleviate these problems. It does not mean that they are free of other problems, especially when they are captured by small special interest groups. But the fact that some corporations are run be evil people does not mean that corporations are bad by design. They can operate differently and for a much greater public good under different circumstances. The same cannot be said of small scale capitalists in a free market system.
Wojtek