Every measure like that introduces safety risk into the critical air traffic control system by increasing the odds of data inconsistencies and other things going wrong. I don't believe it's worth it just to preserve the privacy of billionaires and corporations.

Of course not, but what is the risk here to actual traffic? the plane still transmit its location so others can see it, they simply can't know the exact instance. Seriously asking out of curiosity.

The aircraft's type is not part of ADS-B Out data, it has to be looked up in a database using the hex code. This has implications for aircraft separation, as heavier aircraft produce more turbulence that can be harmful to smaller aircraft. A bad or missing weight category caused by something like PIA having a code collision or a failed update could lead to a fatal accident if the separation for a small aircraft is used for a large one.

A small risk, and something that could be mitigated, but still there nonetheless.

The proposals to encrypt ADS-B data, being driven by corporations and wealthy individuals, are more risky in that they add key management to the mix and make it much more likely that something will go wrong and cause widespread ATC failures or aircraft going dark on ATC displays and in collision avoidance systems at critical moments. Especially as there'll be a mix of encrypted/non-encrypted transponders for decades to come.

Presumably, just aircraft IDs would be encrypted, and not data that is safety-critical for collision avoidance? Things like callsigns (which can be changed each flight and don't necessarily have to be the aircraft's registration) and weight category could also be added, unencrypted, so that ATC screens wouldn't go dark if there was some sort of key management failure.

There is also an argument for some sort of cryptographic signing of ADS-B messages in order to prevent spoofing.

Aircraft IDs are used for type lookups and uniqueness. Callsigns are already in the signal and must be the registration for anything other than commercial or military flights, as they're registered and there's a process for allocation. Weight category and other data being added would require a whole new revision of the standard and will not reach most systems for decades.

Is all of this really necessary when billionaires have other means at their disposal to avoid scrutiny? Why add risk and complexity to a critical system just to make their lives easier?

Spoofing is not really a useful attack vector, for various reasons. In any case it's also not something that can easily be retrofitted for the same reasons, in that it takes decades to update these systems.