Putnam and Campbell conclude that religion is the glue that holds American society together. Most people, of all faiths, think all good people go to heaven (or the equivalent good outcome).
Even the "intolerant tenth," who think there is only one true religion, think religious diversity is good for America.
So why doesn't religion divide America, as it does other nations? Because nearly all Americans have friends or relatives of other faiths in their social networks. Putnam and Campbell call them "Aunt Susan" and "my pal Al."
The conclusion that Putnam and Campbell reach at the end of American Grace:
“Devotion plus diversity, minus damnation, equals comity."