Obtaining a monopoly is itself a competitive activity, so that, at the margin, the cost of obtaining a monopoly is exactly equal to the expected profit of being a monopolist. An important corollary of this assumption is that there are no intramarginal monopolies-no cases, that is, where the expected profits of monopoly exceed the total supply price of the inputs used to obtain the monopoly. If there were such an excess, competition in the activity of obtaining the monopoly would induce the competing firms (or new entrants) to hire additional inputs in an effort to engross the additional monopoly profits. (Posner, 1975)
Social Cost of Monopolization