But the principles of laissez-faire have had other allies besides economic textbooks. It must be admitted that they have been confirmed in the minds of sound thinkers and the reasonable public by the poor quality of the opponent proposals – protectionism on one hand, and Marxian socialism on the other. Yet these doctrines are both characterised, not only or chiefly by their infringing the general presumption in favour of laissez-faire, but by mere logical fallacy. Both are examples of poor thinking, of inability to analyse a process and follow it out to its conclusion. The arguments against them, though reinforced by the principle of laissez-faire, do not strictly require it. Of the two, protectionism is at least plausible, and the forces making for its popularity are nothing to wonder at. But Marxian socialism must always remain a portent to the historians of opinion – how a doctrine so illogical and so dull can have exercised so powerful and enduring an influence over the minds of men and, through them, the events of history. At any rate, the obvious scientific deficiencies of these two schools greatly contributed to the prestige and authority of nineteenth-century laissez-faire.
Let us clear from the ground the metaphysical or general principles upon which, from time to time, laissez-faire has been founded. It is not true that individuals possess a prescriptive natural liberty in their economic activities. There is no compact conferring perpetual rights on those who Have or on those who Acquire. The world is not so governed from above that private and social interest always coincide. It is not so managed here below that in practice they coincide. It is not a correct deduction from the principles of economics that enlightened self-interest always operates in the public interest. Nor is it true that self-interest generally is enlightened; more often individuals acting separately to promote their own ends are too ignorant or too weak to attain even these. Experience does not show that individuals, when they make up a social unit, are always less clear-sighted than when they act separately.
We cannot therefore settle on abstract grounds, but must handle on its merits in detail what Burke termed “one of the finest problems in legislation,” namely, to determine what the State ought to take upon itself to direct by the public wisdom, and what it ought to leave, with as little interference as possible, to individual exertion.
John Maynard Keynes, The End of Laissez-Faire (1926)