AP Photo

Ideologically driven and historically ignorant violence is not an Islamist monopoly. Sometimes postmodern, politically correct Westerners can be every bit as zealous - and as potentially destructive of the past - as premodern Islamists. One of the joys of visiting California’s Yosemite Valley is a series of historic arched bridges that span the Merced River on the valley floor. One, the 80-year-old Stoneman Bridge, is an architectural masterpiece and a tribute to Depression-era ingenuity and artistic elegance; the sister Ahwahnee Bridge and Sugar Pine Bridge were likewise designed to combine functionalism and beauty. All are used daily, are appreciated by thousands of visitors each summer, and now are listed as endangered treasures by the National Trust for Historic...