Shared norms and beliefs do not necessarily predict a shared pattern of inference. Although it is often assumed that people who share the same beliefs and values will most likely draw the same conclusions given the same evidence, there is reason to believe that argumentative divergences can and do occur quite readily among groups who share common creeds, texts, and orientations. Michel Billig (1996) has provided extensive analysis of this phenomenon, including discussion of religious communities who argue endlessly over the meaning and implications of their shared texts, norms, and histories. Ironically, the plenitude of their shared beliefs and norms provides easy fodder for more, not fewer, arguments. Quite simply, in communities who share many beliefs and norms, there is more on the table to argue about, and more fine points to consider. Thus the possibilities for contestable assertion do not seem, necessarily, to be reduced by the sharing of concepts and norms of reasoning. The feature that Billig emphasizes in such cases is the implicit two-sidedness of any argument, and the lack of guarantee that there will ever be a bottom line in sorting out disputed claims.
Lyne, John. 2012. “Having ‘A Whole Battery of Concepts’: Thinking Rhetorically About the Norms of Reason.” Social Epistemology Review and Reply Collective 2 (1): 143-148.
One likely advantage of shared beliefs and values for argumentative diversity, of course, is that everyone can agree about what's an important topic to argue about. The person with which you are least likely to argue much is the person who thinks that the things you want to argue about are in reality pointless to argue about. So where shared beliefs and values are lacking, a lot of energy gets expended simply trying to work out what the worthwhile topics of argument are.