Let me approach this from a purely historical angle; First; to make the broad generalization that "everyone lived in small self-contained communities" is frank

Let me approach this from a purely historical angle; First; to make the broad generalization that "everyone lived in small self-contained communities" is frankly laughable, assuming the statement isn't taken out of a context that constrains the "everyone" in that quote. Yes, we didn't have the megacities we have today, but you certainly couldn't say "everyone would know who was dating the baker's daughter" somewhere like Pompei or Tikal. Secondly, even if you want to argue the cities case, national/international trade has existed almost as long as established civilization. It would have been VERY easy to move among trade lanes and find a new home, if your "anonymity" had been compromised in a way you didn't like in one place. Starting with a truly clean slate in the modern age is FAR more difficult; I'd argue that we've been slowly shrinking the degree of anonymity one can re-achieve. (there is good historical precedent for movement via trade if you look at, to pull one example off the top of my head, certain trade-oriented tribes in central-south native american culture. They would regularly spread out to other small groups in which their past was as anonymous as could possibly get; there is good record of american settlers traveling with them to embed themselves in the admittedly small tribal cultures, but the size alone does not moot ones ability to seek anonymity.)