That is fucking stupid, half of what they say is either a lie, stupid or FUD. Why do people want e-mail to be something that it isn’t? We all know web based services aren’t great for encryption, stop trying to make the impossible, e-mail should be used for service authentication and that’s it.

If you create a ProtonMail account through Tor (which btw .onion addresses just take a bit of the load from nodes unto the server, it doesn’t “enable your authentication”, otherwise Tor would be pointless because you could only browser a very small amount of .onion sites) and use it to create an account on sellillegaldrugs.com, and somehow the CIA wants your e-mail data, the only thing they’ll get is the sign up e-mail and its metadata, which can’t be used alone to identify you unless there’s another exploit or something attached to it.