David E. Campbell and Robert D. Putnam ask how America can simultaneously be religiously devout, religiously diverse, and religiously tolerant. They argue that America's relative religious harmony lies in the frequency of “religious bridging.“ Almost all Americans have a friend or close family member of another religion, and these personal relationships keep America's religious melting pot from boiling over.
Campbell, David E., and Robert D. Putnam. "America's Grace: How a Tolerant Nation Bridges Its Religious Divides." Political Science Quarterly, 126.4 (Winter 2011): 611-640.