Earlier quoted context omitted.
with that argument TLS would be insecure, because there are insecure TLS implementations.
That's not the argument, it's that it's a bad design repeatedly shown to be shown to be prone to serious vulnerabilities and it's silly to argue it's not a bad design at yet another such time. People have made serious arguments for all sorts of design problems in SSL/TLS.
the design is not bad per se. pgp is just a bit outdated and needs an overhaul.
And cryptographic serialization is just difficult.