“The problem of the free market, mentioned in the text only in its application to the labour market, is of very considerable importance. Generalizing from what has been said in the text, it is clear that the idea of a free market is paradoxical. If the state does not interfere, then other semi-political organizations such as monopolies, trusts, unions, etc., may interfere, reducing the freedom of the market to a fiction. On the other hand, it is most important to realize that without a carefully protected free market, the whole economic system must cease to serve its only rational purpose, that is, to satisfy the demands of the consumer. If the consumer cannot choose; if he must take what the producer offers; if the producer, whether a private producer or the state or a marketing department, is master of the market, instead of the consumer; then the situation must arise that the consumer serves, ultimately, as a kind of money-supply and rubbish-remover for the producer, instead of the producer serving the needs and desires of the consumer.
Here we are clearly faced with an important problem of social engineering: the market must be controlled, but in such a way that the control does not impede the free choice of the consumer and that it does not remove the need for the producers to compete for the favour of the consumer. Economic 'planning' that does not plan for economic freedom in this sense will lead dangerously close to totalitarianism.
Karl Popper, 'The Open Society and Its Enemies' (note 26 to chapter 20).