Under extreme socialism, think Orwellian levels, definitions of words are inverted. So the argument would be, if one believes we're already deep into Orwellian territory, that what most people think of as some kind of extreme capitalism because we have these large, unchecked corporations running around, is actually extreme socialism, aka fascism: the merger of corporation and state. And that's the reason these companies have gotten so large and unchecked. That we're not in a free market, but rather dealing with cartels that have grown like weeds and enforced their monopolies through violence through co-opting and/or cooperation with the state.
That's the idea, not trying to argue that's the case. Just giving a possible answer to your question. In reality we're all in a completely free, survival of the fittest-type situation. We're all gonna die someday and all that. It's just that society provides some nice illusions wherein we can debate about whether we're socialist or capitalist.