It was at the end of The Golden City, the last of the Fourth Realm trilogy, that J12H made a privacy argument that I thought had something going for it. In Gabriel's climactic broadcast, he says:

And some of you may ask: 'Is there any value to privacy?'
All new ideas are dependent on some kind of mental privacy - the potential for peace and reflection. The Vast Machine provides information about us and gives the authorities a wide variety of ways to manipulate our thoughts with a subtle power. Everything we hear and see can be shaped to create certain prejudices. Free will - that is, our ability to make real choices about significant issues - becomes an illusion. Gradually, we are surrounded by targeted messages that destroy the opportunity to make our own decisions.

Powerful stuff. A strong argument against my view that privacy can be abandoned. My response is that 'peace and reflection' requires preventing write access, not read access to one's brain. It's true that the more people know about us, the easier it is to manipulate us. But it's at manipulation itself that we should draw the line, not the ability to manipulate.