Unencrypted does not mean that the plane avionics will just accept any input without performing plausibility checks.

Even for "plain" (i.e. unaugmented) GPS, there's countermeasures, starting from simple physical ones (e.g. directional antennas leveraging the fact that GPS satellites are usually located above the airplane and not below or inside it), up to complicated logical filters checking all inputs for plausibility and rejecting suspicious signals and resulting position fixes.

Galileo even supports message authentication, which thwarts everything other than (very sophisticated) real-time signal relaying attacks: https://berthub.eu/articles/posts/galileos-authentication-al...

Subverting the positioning is different than denying the capability entirely through a higher power transmitter. If you require precise positioning to land and don't have it, kinda moot whether you're faking messages or overpowering. During VFR, not a concern. During IFR, low viz, etc, that is where capability loss is potentially material.

https://www.cnet.com/culture/truck-driver-has-gps-jammer-acc...

(aware of military receivers that can receive jam resistant signal, but that is not what commercial applications have access to)

True, which is why almost all airports have multiple different types of approaches, including ILS (which is directional and very high power transmitters in a specific location to jam).

The possibility of a large-scale GPS outage or jamming event is definitely a threat scenario that's being considered by aviation safety agencies. For example, here's the FAA's approach for en-route navigation redundancy, which includes maintaining enough VORs to ensure that there's at least one within every 100 nautical miles: https://www.faa.gov/about/office_org/headquarters_offices/at...

Yes, denying augmented GPS capabilities will probably impact operational efficiency significantly, but it shouldn't endanger safety.