There is a very important difference between a subset of the public and the public. The prisoner's dilemma is the basic template for most of that difference. Autonomous subsets of society act in their own interest to the detriment of society, and by extension, their own detriment.

The individual fiduciary responsibilities of each corporation create a wasteland in aggregate. No one wants to fucking live in this apocalyptic hellscape of advertising, manipulation, deception, and corruption that we have created for ourselves, but no one is willing to give it up either because they have no power to force everyone else to. In order to solve the prisoners dilemma, you do, in fact, need a monopoly on force. You need the entire public, and the will and capability to punish defectors.