I'm all for the inclusion of sociology (and ethnology, by the way). This could become a human sciences site, and get a new name like "humanities.SE".
Sites like Stackoverflow are incredibly broad in scope, in fact it is incredibly difficult to post a software-related question that is offtopic there.
I think that most psychologists and cognitive scientists have a much too narrow perspective and limited methodology in their research. We want to understand human behavior, how can we exclude other disciplines that deal with the same questions, and still believe we are getting a clear picture? In the course of its establishment as a separate discipline, psychology has cut itself off from philosophy, pedagogy and sociology. Now that psychology has a stable standing, it is time to re-connect and integrate the disparate perspectives.