Alright, but that is just theory. The reason you'd want a text protocol is so that humans could read it. Once you secure the protocol, you can't read it without a machine to help you.
Well, by the same reasoning I "can't" easily talk HTTP because I can't talk TCP, IP and 802.3 - they're all binary.
This is exactly why I wrote "high-level protocols". With just a telnet client I can talk HTTP, FTP, SMTP, IMAP, POP3, IRC and so on. And the machine just needs to handle lowel-level details.