The contribution by Luciano Lanza to the Reimgining Society project is a well argued and compelling articulation of the mutualist position and I want to point out both some of the strengths and some of the weaknesses in his argument.
In general these market-libertarian positions rely on theoretical underpinnings provided by anarchist thinkers who are convinced that all efforts at "planning" revert to bureaucratic inneficiency at best and totalitarianism at worst. In this view democracy too often morphs into the loss of individual autonomy and freedom. Using both conceptions of pre-capitalist( ancient) markets and the direct historical experience of "socialism" of the last century, mutualists argue that authority, concentrated power and hierarchy cannot be avoided unless free competition replaces planning as an organizing principle.
My own experience in the bazarres of southern Europe and medinas of North Africa would seem to suggest markets could comport with certain "essential" social human characteristics. In this setting the "bargaining process" over consumer goods did contain a certain element of sociality as we leisurely and patiently, often over tea and keef, negotiated over price. There was mutual respect and even solidarity. the nature of the exchange seemed to affect the quality of relations.
The contradiction seems to arise when we leave consumer markets and enter labour markets, where "mutualistic competitiveness" gives way to exploitation. In Marxian terms , it is axiomatic that the value produced by human labour-power exceeds the cost of producing that labour-power with the excess going to the increase of capital. In other words, capitalist relations reduce human capacities to a commodity which, even when it fetches its exchange value in a free competitive market, recieves less than it adds to the value of the product, increasing the accumulation of capital which is then used to further dominate those whose labour it buys. Add to this the alienating and atomizing effects of "commodification" and it is difficult to see how class and conflict are not an automatic result of such a relation.
Mutualists such as Lanza argue that certain "interventions" can "soften the impact" of competition and that the "role" of economic relations within the entire (pluralistic) sphere of relations can be reduced such that solidarity is retained. I would argue that the regression of European social democracies as well as the current experience in Venezuela show that simply changing labour relations ( strong unions, cooperatives, worker owned /managed enterprises) while keeping a profit system and markets ,is an unsuccessful strategy. Competition is less an "essential" human trait than a nurtured one and that Participation could replace it as an operating principle.
Unless there is a way ( as yet undeveloped) to separate consumer markets from labour markets , "free" exchange is an oxymoron and humans capacity for free, concsious and creative activity can only be realized through the political, deliberate process of participation.