In the Brownian worldview, all religions — even Roman Catholicism — have the potential to be wonderful, so long as we can get over the idea that any one of them might be particularly true. It’s a message perfectly tailored for 21st-century America, where the most important religious trend is neither swelling unbelief nor rising fundamentalism, but the emergence of a generalized “religiousness” detached from the claims of any specific faith tradition.
What is so ironic is that this view--that religion is in a separate sphere, one that is only accessible by intuition or sentiment and one that is not verifiable by typical canons of knowing that characterize the rest of the world; hence, all religions actually are useful for "spirituality" or "religiousness" and not for truth--is the fundamental worldview of modernity. This modern worldview developed from the work of Immanuel Kant, who separated Phenomena (the appearance of things verifiable by scientific testing) from the Noumena (the substance of things that are unverifiable and ultimately reside in the mind of God).
The result of Kant's philosophical move was to create a dualistic world that separated science from faith, matter from Spirit. Theologically, this worldview was best articulated by Protestant Liberalism, which sought to distinguish "abiding truths" from "changing (theological) categories" and which ultimately tried to cordon off theology from the acids of history. In our day, this generally pervasive attitude that separates truth from religious claims is actually based on a worldview that is only about 200 years old and which finds its best proponents among mainstream Protestants who have generally set aside the historically-based truth claims of Christianity.
What is odd to me is that the upshot of Dan Brown's work has not been to turn people back toward mainstream Protestantism, but to turn people away from the church (and Christianity) completely. It reminds me of C. S. Lewis' The Last Battle in which the cynical creation of Tashlan ultimately inoculates the Narnians against the truth of Aslan--because truth and reality itself was drawn into question on the behalf of a pluralistic, general religiosity, the Narnians would not and could not believe.
At the end of the day, our best hope--both in answering the claims of Dan Brown and the worldview behind it--is not simply to debunk his historical claims point by point (as several excellent books did after The Da Vinci Code movie came out), but to question the essentially modern, Kantian worldview that helps Brown make sense. After all, Christianity is faith based on historical facts, none more important than Jesus Christ, the Son of God, died for sinners on Calvary and rose bodily the third day from the grave. If that is not true in a way that destroys the dualism between phenomena and noumena, then we of all people are most hopeless.