Laissez faire promotes social strength by rewarding the strong and punishing the weak Laissez faire means the government should not interfere in the economy. It doesn't advise people not to cooperate. — frank
Treating the "economy" as a natural condition is problematic. The argument against planning and control of markets has been made by such as Hayek and Milton. They argue that withdrawal of control serves social ends such as the expansion of prosperity and the decrease of tyranny. Whatever one thinks about those policies as means to their stated ends, they both assume that one needs to overcome "natural" reactions to make them effective in terms of outcomes. They embraced the values of the progressive citizen as articulated by their interlocutors but claimed those interlocutors were defeating themselves through attempts to directly create certain conditions.
Introducing the ideas of Social Darwinism into the discussion is a matter of offering too much and too little at the same time.
Those ideas are too much in the way they frame the "Letting it play out" argument of economists to be some kind of acceptance of a natural order. Hayek is closer in spirit to Hobbes than Rousseau regarding the social contract. Hobbes' way to stop the "natural" war between individuals is to agree to an order that binds them together. Rousseau sees nature as something order screwed up. In this battlefield of differing presuppositions, the introduction of evolution is a step back from the fray. Being a species is relationship to other species. The existential crisis of being whatever form of life you happen to be is no longer confined to the struggle within a kind you happen to be suffering but is connected to whatever Life is and the other stuff that is alive.
That last observation shows how the idea of Social Darwinism is too little for the issue under discussion. The biggest fish in the sea, if one is to look at our existence from the point of view of evolutionary development, is Ecology. The "survival of the fittest" idea only makes sense in a region where the "selection" is not a search for the "fit" but an acceptance that the balancing of life forms is well beyond the matter of what we highly prize. The evolutionary perspective calls for humility in the way Spinoza called for when asked to decipher the ends of the Creator.