That has very little to do with the point I'm making, and it is not a point I am debating, so I wonder why you reply like this.
In fact, I would agree with what you say, as long as there are other enforcable rules that limit the total free-for-all a free market at its worst could turn into. I do not believe an unconstrained free market will automatically lead to the best solutions, or even set the best prices (best for whom?).
Any viable constitution will have to take into account that not everybody supports the same economic thinking, or even believes that there is a working economic theory out there at all. Trying to come up with an economic theory from assumptions and reasoning alone is rather medieval. If there are no testable hypotheses, or real-world data is ignored, such a theory is without worth.
I think anthropology is a better place to look for inputs for a constitution than economic theory, and I suspect no good will come at all until we replace competition with cooperation.