An issue I would forsee with the requirement of encryption by the FCC, and the issuance of a master code by the same FCC, is what would it cost amateur radio operators to obtain the master code? You have already ruled out the possibility, in your scenario, of the radios coming preprogrammed with the master code, and, as a realist, I do not see any branch of the federal government giving out this type of information freely. So, there would most likely be a fee that would have to be paid to the FCC to get the master key. Also, your scenario seems to preclude the possibility of them giving the information out freely since, if they did, a member of the general public could buy the radio, get the free code, and continue listening. Your scenario has ruled out that possibility. Of course it would only be a matter of time before people started selling the code themselves (cheaper than the FCC of course to make a profit) or simply gave it out to their friends, so the FCC would have to change the master key from time to time. Another fee to get the new one? The same goes with the differs. How much would a club charge for the differ key? Who would they allow to have it? And most importantly exactly what are they discussing that should not be heard by the general public?
As it is, however, the issue at hand is the use of encryption in an emergency, etc. not the requirement of encryption.
Christian KF4ZMB