1. You can create throwaway PGP keys, it's not like they can definitively identify you 2. You can encrypt messages for target PGP public key(s) without actually signing them

It's a good way to prevent people from snooping on your messages. Why do you think it's a bad idea?

The newer protocols for encrypted messaging like Signal are intentionally less weak than PGP in order to give plausible deniability. Specifically, the other person in the conversation can forge messages from you inside it.

because it works but some people think it getting in criminal hands is too big a price.

If you want to stay whitehat and avoid jail, committing crimes is a bad idea. For criminals, blackmailing is part of their M.O.

There's an international market of brokers for zero days, but this specific vulnerability is less in demand.

I doubt that the information found at Facebook legal team could be used by nation-states (but perhaps I am not thinking creatively enough). I can imagine it being used as leverage by a nefarious nation-state, or informational by anti-trust dept. but it would be thrown out of court (therefore only viable for parallel construction). In the case of leverage the nefarious nation-state would feel the wrath of Facebook and/or US government. A country where Facebook has near zero adoption and already on bad terms with USA while within power vacuum, perhaps. Russia has Vkontakte, North Korea and China don't use Facebook either.

Regarding PGP, you don't have to use your real name. You can use an alias. You can sign each other's keys at a crypto party.

I had to chuckle at your comment (at first glance it does seem foolish), thinking about it a little more however, I realize that there is a good reason to why they do it, and if you are careful enough you can probably evade the negative consequences. I guess you have to know what you are doing.

I mean you would be using a live OS and set up a key on that instance so it’s always a new identity, if you choose not to persist it, that service just doesn’t let you message any other way.

It would be much harder to mix identity with your clearnet pgp, if that’s what you were thinking, as the machines would air airgapped or the other ones simply off if you are using the same computer to boot the live os

Any other configuration is just lazy