Earlier quoted context omitted.
Signing everything is not terrible advice. But here the problem Fred is trying to solve is very simple. He is an investor in mirror.xyz and needs to make his money back. This is the only reason someone interested in signing something would also ask you to go through the hassle of using a blockchain.
To add to this a bit - I do think an embedded steganographic-type “signature” of chatgpt output could be enormously valuable - without it we can wave goodbye to the efficacy of things like school assignments. Such a signature is very different than a typical cryptographic one we have today however. But I expect instead of embedding such a signature they will just save hashes of generated content and sell a billion do…
OpenAI did hire somebody who is investigating watermarking the output of models like GPT-3, so it's definitely possible.