Sure, but a police operation surely could attempt to swap the book cipher out for a compromised one, no?

I think the idea that communication ought to be categorically out of reach of intelligence is very novel. I don't think it was even conceivable decades ago that, with legal justification, intelligence could not hack or be completely locked out of the communication of some network. For criminals who are savy enough, tech has made it much harder, not easier for the government to do their job.

I think there is also a very paradoxical side-effect. A harmstrung government may resort to outsourcing its intelligence work. I read a story about private firms in the US collecting license plate information and selling it back to the police. Clearview AI is certainly another example. If the agencies are limited, there is a real chance of both ineffective policing and a huge unregulated surveillance grey market. I would rather equip the government with enough capacity, but strong legal checks.

Legal checks are a mile-long leash, no matter how strong the cord. This is exchanging freedom for security, since a backdoor like this doesn’t require breaking glass.