But no more insecure than the original interaction. It's a generic problem with anonymous public key crypto. Hence the stuff with the twitter fingerprint.
Twitter fingerprint was for Laura's key. Micah's public key was already published and already signed by other known people, so Snowden was sure than only Micah can read the e-mails for Micah, unless somebody hacked Micah's computer, when all bets are off and GPG doesn't help anyway.
Yes but the Man in the Middle could very well be the author of the e-mail to Micah, didn't he? Micah would then have tweeted a fingerprint leading to eavesdropping.
No, not "eavesdropping." The fingerprint is only a fingerprint and only of the public key. It doesn't give new secrets away. Nobody can use it to read any mails of somebody else.
