I generally agree, but intelligence groups have to first find the signal they want to monitor. Modern steganography techniques coupled with the free randomness you get from the physical world gives you much to work with. And that's assuming common tech will be used.

Also, designing a secure general purpose messaging system is much harder that designing a system tailored for a specific use case.

Banning encryption by law is like demanding, loudly, that people not talk behind your back. Some will listen, and some will not. Only legitimate users and use cases will suffer.