Even if FB / WhatsApp doesn't currently have such a capability, there's no legal guarantee they couldn't be compelled to add it, thereby putting them in conflict with language that didn't include that clause.
Afaik, case law is murky over whether creating new code qualifies as speech (illegal to compel) or facilitating legally-approved wiretapping (legal and required).
More interesting is what happens if someone gets a new phone. In that case (if I understood correctly) they might ask for the sender to resend the messages with a different key. If they really are forced to add a backdoor then that's where I would fit in a MITM attack, as it is limited in scale and detectable when used excessively.
Pretending and using obfuscated language to lead the reader to believe otherwise is disingenuous.
>WhatsApp has no ability to see the content of messages or listen to calls on WhatsApp. That’s because the encryption and decryption of messages sent on WhatsApp occurs entirely on your device. Before a message ever leaves your device, it's secured with a cryptographic lock, and only the recipient has the keys.[...]
>A search warrant issued under the procedures described in the Federal Rules of Criminal Procedure or equivalent state warrant procedures upon a showing of probable cause is required to compel the disclosure of the stored contents of any account, which may include "about" information, profile photos, group information and address book, if available. In the ordinary course of providing our service, WhatsApp does not store messages once they are delivered or transaction logs of such delivered messages, and undelivered messages are deleted from our servers after 30 days. WhatsApp offers end-to-end encryption for our services, which is always activated
Very interested to see what their response is and if their promise holds that they do not have technical access to content but merely to account information.