Humans are passionate creatures. Our passions drive us, gives us a sense of belonging, and unite us as few other things can. Still, there are only a couple of passions that have been constants down the ages, passions that people from every place and culture can agree on. Love is one, but another is that "those no-good bastards over there are trouble." Of course, we quibble endlessly over the exact definition of "those" -- every culture, pretty much, has had a different group in mind. But the singular fact of prejudice per se was as recognizable in Ancient Greece, Rome, and Samaria as it is...