"I was very closely involved for the integration, had full access to the source code, did plenty of review, and have a lot of confidence in the engineers that are maintaining it.
There are plenty of engineers in the world who are capable of inspecting the binaries they're distributing, so it would be incredibly risky of them to inject surveillance code client side."
I guess that the governmenet doesn't even need a backdoor in the Facebook app... Since Google has admin privileges on your device and is in bed with the NSA, they could go that route instead.
Behind WhatsApp's E2E encryption is the technology from Signal / Open Whisper Systems, which is developed in the open, the work on WhatsApp being done in partnership with them, see: https://whispersystems.org
Of course, it's not totally trustworthy, because in the end it's still a proprietary app, distributed as a binary blob, connecting to proprietary servers, for which you can't have access to the source code and in spite of any well meaning partnerships, they can always push an update that undoes all of that.
But you know, at this point that's still better and more trustworthy than other mainstream alternatives. So now I have WhatsApp installed.
Then again, Moxie said he himself oversaw the implementation of the encryption and that he has trust in it...