The logic goes that public planning always starts from a distorted, fractured image of reality that has poor predictive power. The effects of the plans themselves have ramifications for the future, and since these are sometimes unpredictable the whole edifice of planning leads to chaos and disaster.
In contrast, the "magic" of the market-place is that millions of individuals, without planning enmasse, are able to coordinate their actions through the price system, in a far more organic system, with millions of inputs and responses, that produces far more efficient outcomes.
However, it must be remembered that the planning societies don't have too bad a record of economic growth and social security. True, they often appear to be lurching from one crisis to the next, but such is life -- isn't it?
Meanwhile the market itself always careens from boom to bust, euphoria to depression. When these millions of autonomous actors make their millions of independent decisions through the price mechanism, sure things can be "coordinated " for awhile. Just like bureaucrats or democratic societies can coordinate resources to achieve a stated objective. But as resources congregate towards accomodating temporary demand, they can drive down the prices of some things, run up the prices of other things, and if it all ends in a "correction" that destroys fortunes and lives, why isn't this portrayed in the same way that planners' unintended effects are? Why aren't market corrections treated with the same disdain as planners' failures and incompetence?