Are Catholics too "mainstream"?

Here's a good post, by Peter Nixon, over at Commonweal.  He's commenting on a recent study of American Catholics, conducted by the Barna Group, which "concludes that Catholics are more or less indistinguishable from the general public with respect to many social and cultural attitudes."  (See also Ron Sider's "Scandal of the Evangelical Conscience".)

Peter is concerned, but skeptical, and -- I think (notwithstanding my strong concern for Catholic distinctiveness) -- with some justification:

I'm not trying to ignore the massive amount of evidence out there that there has been a marked decline in Catholic religious practice in the last half century. The evidence--from many sources other than Barna--is overwhelming. The finding that concern for the poor is not more evident in the Catholic population than in the general population is certainly cause for concern, as are some of Barna's other findings.

But the overall tone of this document irks me, as it seems to suggest that Catholics are not good Christians primarily because they don't think and act like Evangelical Protestants. . . .