Whoa. Way to completely miss the point. Facebook messenger and WhatsApp are completely different apps. WhatsApp is using the Signal protocol which is pretty much the best there is at the moment. All the messages and calls are end-to-end encrypted with the kind of crypto nerds used to only dream about. Mass surveillance is not possible (even for Facebook) with WhatsApp, because the attacker would need to do a MitM attack on all the discussions, which is easily detectable. Another option is to install malware on the phones and read the messages there, but that would be a targeted attack anyway.
There haven't been any proven breaches of the Signal protocol and I dare you to prove me wrong. "Facebook is evil so WhatsApp must be broken" just doesn't fly.
As far as the security community is concerned, the biggest weakness in WhatsApp is that MitM notifications aren't on by default. Otherwise the app and the crypto is solid. It's easy to say that WhatsApp is compromized because of $reasons, but if you have actual proof of a breach, it will absolutely be headline news, so cough it up. You'll be a infosec rockstar (for at least a week).
Also - open source doesn't automatically mean that the application is safer than closed source. Implementing crypto is hard. You can mess it up in bunch of different ways. It doesn't help one bit that your source is available if nobody with decent qualifications has ever checked it.