One thing is to transfer information from person A(Alice) to person B(Bob) without any other party E(Eve, eavesdropper) deanonymizing A or B or blocking or tampering the information, but another thing is to verify that the information that might be transferred or published even to a wider audience is true, accurate. It might be that Alice is not lying to Bob, but Alice is just stupid or drunk. On top of that there is the identity theft problem, where someone has gained access to Alice's private keys without the Alice knowing about it. On top of that the Bob might be stupid enough not to understand the transferred information. For example, it is impossible to warn people about radiation threats, if people do not know, what radiation is.
On top of that, more deferential people allow their identities to be robbed: "Tell Bob the statement W or we will shoot You or Your baby or Your dog." Codewords won't work with people, who drown in emotions or reveal that they have noticed a codeword, just like they won't work with little children. People, who are psychologically incapable of not loosing physical objects in their peaceful daily lives, will probably loose codebooks and decryption devices even without any adversary trying to get those items from them. The task of managing private keys must not be given to a person, who looses things or is otherwise too unorderly for that task.