Try as we might to remind ourselves that the Catholic church isn't Microsoft and that quantitative measures of success or failure don't always correspond to the logic of the Gospel, most of us take that lesson to heart only selectively. Some Catholics can't resist touting the huge crowds at World Youth Day as an endorsement of their version of orthodoxy; others cite polling majorities in favor of reform on birth control and other issues as proof of the sensus fidelium.

The most powerful recent instance of that temptation has been Catholic reaction to the 2008 "Religious Landscape Survey" from the Pew Forum, which documented a remarkable fluidity in religious affiliation in America -- almost half of American adults have either switched religions or dropped their ties to religion altogether.

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