Methods like spread-spectrum communication are allowed. It's not the same as encryption, but it it similar in that people without knowledge of the frequency hopping pattern are not capable of receiving the transmission [2].
Ultimately I'm not particularly invested in permitting encryption in amateur radio - my personal involvement is mostly homebrewing simple equipment - but I'd consider it a plus. I doubt it'd displace public participation around local repeaters and the existing radio activity.
1. https://www.arrl.org/about-arrl
2. Well, if they have an SDR with a wide enough bandwidth they can receive spread spectrum communications. And with modern SDR's that probably not that rare.