The supreme and inestimable merit of the exchange mechanism is that it enables a vast number of people to cooperate in the use of means to achieve ends as far as their interests are mutual, without arguing or in any way agreeing about either the ends or the methods of achieving them.
It is the “obvious and simple system of natural liberty.” The principle of freedom, where it is applicable, takes other values out of the field of social action. In contrast, agreement on terms of cooperation through discussion is hard and always threatens to become impossible, even to degenerate into a fight, not merely the failure of cooperation and loss of its advantages. The only agreement called for in market relations is acceptance of the one essentially negative ethical principle, that the units are not to prey upon one another through coercion or fraud.
-Frank Knight ( On the History and Method of Economics)
A further note by Prof Don Boudreaux:
Note that for two or more persons to have interests that are mutual is not necessarily, or even normally, for those persons to have interests that are the same. It is, instead, for each of those persons to have interests that can be furthered by his or her helping to further the interests of the other person or persons. The owners and suppliers (including workers) of Whole Foods supermarket and I have interests that are not the same, but that are indeed mutual: each of us helps the others further our own interests by trading with each other.
