Karl Marx
Karl Marx's Capital argues that free markets do not create equitable wealth, but mask a system of exploitation driven by the extraction of surplus value from human labor.
In a capitalist society, the social relationships between people are disguised as material relationships between things, a phenomenon known as commodity fetishism that masks the human labor embedded in products.
The exchange value of a commodity is determined by the socially necessary average labor time required to produce it, rather than by its mere usefulness.
Profit originates not from the equal exchange of goods in the market, but from surplus value, the extra unpaid labor extracted from workers after they have produced enough to cover the cost of their own survival.