Casilda, I certainly agree that novels don’t have to explain themselves in order to be good, but the ideas must feel coherent and must provide us with the allusion (and possibly illusion) that this world could work. Throughout the novel, I kept being broken out of this reality by questions of human nature. If you are being attacked by someone and the only person around is in the other city, nature will demand you breach for self-protection. If a dog enters one city from another and knocks you down, that would be Breach. Driving requires that you watch for other drivers while trying to appear like you ignore them.
The whole concept is little more than Fascade if you think about it. Everyone Breaches every day, but have to pretend that they don’t . You have to see them in the corner of your eye as to not run over them, but pretend they are not there. These are stupid rules that have no social, economic or practical purpose. Even in the middle east where certain countries require women to hide any sign of skin, the purpose is religious (and to an extent, meant to control women).
Normally I would put it in the realm of Twilight Zone, but Mieville isn’t using this device to tell a larger point or to even explore the psychology of such a life as this, but seems to have it there just to have a strange society. It just feels lazy.