We may know pornography when we see it, but the business of pornography is a surprisingly elusive subject. Reliable figures about the industry are difficult to come by and widely disputed, but one matter that is hardly debatable is that pornography is a major and ubiquitous enterprise. Porn allegedly accounts for one-third of all internet traffic currently, though the data about actual consumption is unclear. Reports in recent years have suggested that 70 million individuals visit porn sites every week; that among viewers aged 18-24, women watch more porn than men; and that among middle-aged,...