In this section of Boswell's study of shifting attitudes toward (male) homosexuality under Christianity, he explores the question of "why should sexual behavior come in for judgment at all?" as well as the specific trains of thought that were used to support condemnation of homosexuality specifically. He points out that it wasn't a foregone conclusion that Christianity would take this path, and that some of the background set-up for the rise of intolerance was demographic and political rather than philosophical. This shouldn't come as a surprise.