"[For Hobbes] the state is charged with maintaining social stability and preventing a return to natural anarchy... Human beings are thus, by nature, nonrelational creatures, separate and autonomous." -- Patrick Deneed, Why Liberalism Failed, 32
Proto-liberals like Locke and Jefferson and modern liberals like Mises and Rawls all start from a similar place: we are first and foremost human atoms, who only need enter into social groups in so far as it suits our interest to do so. Our original state was as free individuals, who "contracted" into social groups because we saw it was to our advantage. As Deneen notes, "Even marriage, Locke holds, is finally to be understood as a contract whose conditions are temporary and subject to revision..." (33).
Or, as Mises put it:
"The fundamental social phenomenon is the division of labor and its counterpart human cooperation.
"Experience teaches man that cooperative action is more efficient and productive than isolated action of self-sufficient individuals. The natural conditions determining man's life and effort are such that the division of labor increases output per unit of labor expended." -- Human Action
"The fundamental facts that brought about cooperation, society, and civilization and transformed the animal man into a human being are the facts that work performed under the division of labor is more productive than isolated work and that man's reason is capable of recognizing this truth." -- Human Action
"Every living being is naturally the implacable enemy of every other living being, especially of all other members of his own species. For the means of subsistence are scarce. They do not permit all specimens to survive and to consummate their existence up to the point at which their inborn vitality is fully spent. This irreconcilable conflict of essential interests prevails first of all among the members of the same species..." -- Human Action
So, per Mises, humans live in social groups only because they tried both the "isolated action of self-sufficient individuals" and social cooperation, and found the latter suited their self-interest better. Now, those of a religious bent should surely object to the idea that human beings care for each other only to the extent that they calculate that cooperating serves their own self-interest better than being "implacable enemies."
But one need not be religious to see that Mises is spouting nonsense: humans (and proto-humans) lived together in tight-knit social groups long before they could have been calculating the advantages of the division of labor. There never were "isolated... self-sufficient individuals" with which they could compare their "output" as members of a group: isolated humans were dead humans, not self-sufficent humans. And our chimpanzee, bonobo, and gorilla relatives also live in tight-knit social groups, and certainly do not regard the other members of the group as "implacable enemies." (Take a gander at the group of "implacable enemies" pictured at the top of this post!) In fact, cooperation is every bit as much a fact of animal life as is competition.
And methodological individualism is simply the elevation of this false anthropology into a required postulate of any social science worthy of the name.