Yes, if encryption was permitted, there would be a ton of interest...by commercial companies. Non-licensed users would out number licensed ones by huge amounts. It would put an end to amateur radio.
Heck, the authorities have problems policing the bands even without having to deal with crypto.
Abuse would require two licensed amateurs to cooperate to break the law and use the bands for commercial purposes. It would be easier to investigate suspected abuse (compared to unsigned encrypted messages, but not cleartext messages, of course)