In his book "The Enemy at Home," Dinesh D'Souza shows little patience with the leftists who reacted to 9/11 by declaring that America had it coming. And yet, his book is a variant on that theme. It was our cultural decadence, our foul popular movies, music and pornography, D'Souza argues, that enraged traditional Muslims worldwide and moved some to violence. D'Souza is a thoughtful and interesting writer, and many of his observations about the cultural left worldwide, and particularly about the dismaying state of popular culture in America, got vigorous head nods from conservative readers. D'Souza summarizes episodes from a...