Though firm in his fundamental convictions about economic and political liberalism, he was not a doctrinaire; his position can be described as optimism, not naïveté, about the market. He often repeated that laissez faire is not a scientific principle, but just a convenient rule taught by experience.
Certainly subsequent developments of welfare economics have made us more sensitive to externalities and to market failures than he ever was. However, he also was well aware of the importance of the legal framework and a proper regulation for the markets’ well functioning. He deeply believed in equality of opportunities, and accepted a degree of income redistribution.