Free market capitalism is an antiquated form of Capitalism which has been superseded by Imperialism. Per Infrared, those who advocate a return to this form of capitalism today are in fact a kind of Utopian Socialists. What they propose is impossible, since their main obstacle would not be government intervention, but the monopolies themselves. And in order to break up the monopolies you have to expropriate them, meaning any path back to a truly free market would have to take a detour through socialism. And even if we assume this is possible, and that free market capitalism was preferable, Lenin already made the decisive and final point in 1916:
suppose, for the sake of argument, free competition without any sort of monopoly, would develop capitalism and trade more rapidly. Is it not a fact that the more rapidly trade and capitalism develop, the greater concentration of production and capital which gives rise to monopoly? And monopolies have already come into being - precisely out of free competition.[1]
Men at the head of industrial combines tended to agree. In his memoirs John D. Rockefeller Sr. wrote: "It is too late to argue about advantages of industrial combinations. They are a necessity."[2]