It's not hard if you're keybase. GPG isn't known for being based on trusting anybody other than yourself.
Also note that the blogger (seemingly a security expert that people respect on here) I posted just went ahead and displayed their public key, to demonstrate that they're not afraid of Keybase or anybody else having it.
The original discussion was about generating keys from passphrases, which is much, much easier to exploit than what Keybase is doing. The discussion about whether Keybase's usability is worth the security tradeoff is one I'll leave to someone else.
Also note that the blogger (seemingly a security expert that people respect on here) I posted just went ahead and displayed their public key, to demonstrate that they're not afraid of Keybase or anybody else having it.