Because this is the first glimpse of a world where anyone can start a large, programmatic smear campaign about you complete with deepfakes, messages to everyone you know, a detailed confession impersonating you, and leaked personal data, optimized to cause maximum distress.

If we know who they are they can face consequences or at least be discredited.

This thread has as argument going about who controlled the agent which is unsolvable. In this case, it’s just not that important. But it’s really easy to see this get bad.

In the end it comes down to human behavior given some incentives.

if there are no stakes, the system will be gamed frequently. If there are stakes it will be gamed by parties willing to risk the costs (criminals for example).

For certain values of "prove", yes. They range from dystopian (give Scam Altman your retina scans) to unworkably idealist (everyone starts using PGP) with everything in between.

I am currently working on a "high assurance of humanity" protocol.