This paragraph had a problem.
"Marx wrote in his famous 19th century treatise that in order to be profitable, capitalists needed a pool of unemployed workers to exploit. Only by paying labor less than their marginal revenue product -- the additional revenue earned from the sale of the product produced by that worker -- could capitalists extract a profit, Marx wrote."
I believe the quote above is a misreading of Marx. The main source of profit for the system as a whole for Marx is generated under industrial capital by labor being paid less than the value of its labor. (not labor power) Profit is still generated (produced) if labor is paid the value of its labor power. Profit for individual capitalists can be increased by paying labor the labor less than the value of its marginal revenue product (MVP). But if this MVP happens to be equal to the value of labor power (does not have to be at a given instant) the system will not be sustainable without alterations of the system or sources of labor outside of the industrial capitalist system. Marx would never have used the term marginal revenue product. The MVP term is neoclassical and I do not believe would not have but used by Marx. The main point is that for Marx the main source of profit under industrial capitalism in its mature form is not the result of paying workers less than their MVP. For Marx wage labor paid at the value of labor power serves as the main surplus or profit generator under industrial capitalism as long as labor is paid the value of its labor power but less than the value of its labor. The value of its labor being manifested in one aspect by the use values that labor produces. The value of the labour power is determined by the labour time necessary for its production and reproduction. I believe there many controversies interpreting this but the definition in the quotation related to the MVP is not one.
Victor