Free-markets are a function of the kind of freedom those markets are subjugated. Our current version of “free-markets” are subjugated to an oligarchic monism of freedom and therefore yield quite the opposite of free markets.
To achieve the optimal free-market, we must free freedom and steer away from the shoehorn of freedom and instead implement a relativity theory of freedom that takes into account a plurality of freedom.
When we do so, we must understand that freedom can only be maintained when it is supported by paradoxical rules to protect collective freedom. Those rules can be imposed by the participants of the marketplace itself, the government, and most realistically by an equilibrium between both.
So, yes, free markets are only feasible when the need for personal freedom is paired with the need for collective freedom to protect trust in the marketplace. The prevention of collusion is merely one of those protections of collective freedom and by no means the only one.