First off, we need to consider Bickford's distinction that she draws on p. 358 between Lifestyle, Elite, and Security Zone suburbs. We've been talking so far as though all gated communities were equal, and Bickford has been pretty careful to distinguish between them.
But the larger question right now seems to be the chicken-and-egg issue: did our suburban and urban defensive forms spawn defensive attitudes, or originate from them? Her argument, surprisingly enough, is that the spaces seemed to come first. She cites a study by McKenzie on p. 359 indicating that common-interest developments were a developer tool to place more houses on less land. As greater ethnic blending took place in the cities, a great number of white residents fled for those suburbs, so that the desire for "safety" was innately tied to the housing form. From that point, though, the causality is less important — the desire to avoid "others" breeds separation which breeds avoidance which breeds separation, and the cycle amplifies.
The deeper question we'll need to face is how to break that cycle. Many of you have criticized Bickford for not proposing solutions, but she very clearly does so on pages 366-368 in her examination of regional governance rather than the proliferation of tiny jurisdictions. She believes that the research indicates local control leads toward escape as a primary way of dealing with social problems, and that tackling issues regionally or at a metropolitan scale ensures that we can't just shift problems from one neighborhood or town to another.
But you're all professional architects rather than politicians, and I doubt you're looking to change careers. So what can the designer do to break this cycle of separation, avoidance, and fear? Do you have any tools at your disposal to make social change?