Read the passage below, which discusses the evolution of antitrust law. Based on the passage's argument, complete the concluding sentence by filling in the blanks with the appropriate concepts.
During the development of antitrust law in the mid-twentieth century, the 'Structuralist' school of economics heavily influenced judicial decisions. Structuralists posited that highly concentrated markets—those dominated by a few large firms—inherently facilitate collusive behavior and stifle innovation, regardless of the firms' actual conduct. Consequently, courts routinely blocked mergers simply because they would result in large market shares, assuming that market structure invariably dictates anti-competitive outcomes. However, the later 'Chicago School' scholars fundamentally challenged this presumption. They argued that high market concentration often results from superior efficiency and economies of scale rather than illicit collusion. In their view, if a dominant firm achieves its position by offering better products at lower prices, penalizing its mere size actually harms the consumer.