The eNotes rules allow only one question per post, so I had to edit your question. The title of the book, The Devil in the White City, sets up a parallel between good and evil, and every page details the people and events which created both the Devil and the White City. The good things are rather obvious; it is the evil things which are more insidious in this true story.
Dr. Holmes and his systematic killing of innocent women is the most obvious evil, as are all the lies and deceptions he perpetrates to accomplish his murders. He takes advantage of this patriotic and altruistic event for his own evil purposes. Others did the same; though perhaps they were not as evil, they were just as selfish. Architects and others in New York were upset that their city was overlooked as a Fair site, and they were especially outraged that America would be represented by what they saw as the rather crude, wild cowboys of Chicago and the Wild West. Though most of them eventually capitulated, they refused to offer their expertise for the patriotic cause. As you no doubt read, many others along the way took advantage of this project to further their own agendas or gain their own advantages. A World's Fair was (and still is) an opportunity for the host country to display the best of who it is; in this case, though the end result was spectacular, the Fair was an opportunity to also display some of the ugliest and most evil aspects of human nature.