I think we "outsider" engineers forget (or miss the point on) why amateur radio enjoys the spectrum privileges it does: education, technical investigations, research... things that further the art and community. There's a large contingent of hams just listening.

Encrypted meaningless noise on the air would be a "selfish" waste of spectrum incompatible with the neighbourly spirit espoused by most amateur radio organizations and hams themselves, not to mention damaging to the self-policing they're supposed to do.

I alsl expect it wouldn't be "allowed" to persist as a hobby in its current form in many parts of the world if you added the threat of casual encrypted communications, beyond the reach of CALEA-type intercept capabilities into the mix.

The law is probably necessary for HAMs to be self policing.