MSW - you surprise me....to miss Gehring's key theme so completely and over-simplify to this statement:
"Gehring points to the "one neighborhood at a time" solution that is the only thing that will save American culture. But, then why cast "tribalism" as a negative?"

CLUE - there is a significant difference between *one neighborhood at a time* and *tribalism*.

You assume that all US neighborhoods are from one tribe?  

Review this article on democracy (which is the opposite of tribalism):
http://www.texasobserver.org/2348-open-forum-habits-of-democracy/

Key theme - 
 "....ordinary citizens have the capacity to become their own experts, to understand complex issues, and to develop an understanding of their own interests;...analyze issues related to public policy and the role of government, educate themselves, and then go out to teach the issues in their neighborhoods and communities."