This is an important question. It is irrefutable that individual thought and behavior are the building blocks of society; people with "individual psychologies" engage in social interactions and literally construct our society. In turn, the existing social structure (customs, institution, norms) help shape patterns of individual behavior and thought. --A mutually constitutive process.
Having said that, it may seem strange that I completely agree with Carrol: the analysis of individual psychology is irrelevant to the analysis of social structure (or specific aspects of social structure such as class). I know this point is counterintuitive; consider the following thought experiment.
Imagine psychologists develop a machine that can accurately map any person's psychological characteristics (thoughts, interests, opinions, desires, fears). Would this knowledge allow us to understand and analyze the social structure of a particular society? Absolutely not! Sure, the machine may tell us "George over here is one greedy son of a bitch". However, that knowledge cannot explain social structural characteristics such as economic inequality in our society, because a greedy person cannot transform that psychological impulse into economic advantage unless there is a social structure that enables vast economic disparities. In our capitalist society, a greedy person can become rich because there are social conditions that enable economic inequality. In constrast, a greedy person in a hunting and gathering society cannot become rich, because the social conditions of that society do not enable or allow vast economic disparities.
The same argument can be applied to any psychological characteristic: for a person to fulfill a psychological impulse, there must be social conditions that enable that impulse. Even if the person or like-minded people build social conditions that help them all fulfill their impulse, it is still the social conditions that they have built that must be analyzed--not just the psychological impulse that accompanied the change in social conditions!
Now, I'll be the first to point out that there is nothing original or innovative about this line of reasoning; you can find this basic argument in the work of various social theorists and philosophers (e.g., Durkheim, Foucault, Wittgenstein (yes, Wittgenstein!), Iris Marion Young). Note that this takes nothing "away" from psychology; this argument does not imply that the study of psychology is unimportant. Rather, it recognizes that there are different levels of analysis that are valid and useful in different ways. Look at it this way: biochemists can analyze biochemical molecules and processes and come up with valid scientific knowledge without worrying about quantum physics.
In just the same way, social researchers can analyze social structure and come up with valid scientific knowledge without worrying about individual psychology.
Miles
^^^^^^^
CB: Other terminology for this is "levels of organization of reality", or emergent levels. Anthropology or sociology can't be reduced to individual psychology.