If people all started talking through letter mail, you'd get Letter Control, they wouldn't just forget about it because it's not the internet. If the people somehow become smart and coordinated enough to move to some cryptographically-secure method of communication, your government will probably outlaw the equipment and actions associated with using it in the first place instead of trying to decrypt all communications.
The goal is control of information, and the way of doing that is to force everyone to use unsecured communication with no feasible alternatives. I wouldn't expect kid glove treatment with that, unlike speeding or minor shoplifting.
