In 2005 he published a book about Opus Dei, "Opus Dei: An Objective Look Behind the Myths and Reality of the Most Controversial Force in the Catholic Church". Allen said that one of his reasons for writing his study of Opus Dei was that he felt that liberal and conservative Catholics were too often shouting at each other, and he hoped that a book that tried to be fair to all sides would lead to civilized discussion. According to John Romanowsky of "Godspy", Allen's ability to report objectively, without revealing his personal opinion, has been called "maddening".