Note that this argument is even more problematic for OpenPGP-encrypted email, as such email sends all metadata and some message data in plaintext.
I ususally respect tptacek a lot but when it comes to Whatsapp I actively avoid it if at all possible, preferring Telegram even if the crypto is more than questionable. Same goes for mail: I prefer it - even unencrypted - over Whatsapp.
For some of us our treat model is more concerned about Facebook and less about major TLAs.
With Whatsapp I have to expect that all metadata about me - and my friends - are fed into Facebook and datamined from here to eternity and back again or until the end of the world as we know it.
I have little to hide but given the catastrophically bad ad targeting of Facebook (yes, I am still a happily married father, a Java developer, a Norwegian. I don't need ANY more ads for dating websites until I specifically change my profile to let you know, THANK YOU. I would be happy to learn about useful developer tools or underrated fast food restaurants though. I also appreciated the uber ad with bundled coupon in google maps a few weeks ago and tested uber for the first time.)
Given the same catastrophically bad targeting and given that it is the same owner who as far as I know hasn't yet apologised for his remarks about how trusting him was stupid it wouldn't surprise me if is more a WHEN than a IF that Facebook is going to sell everyones data to insurance companies, support scam call centers etc.
I am not trying to use a secure messenger. I am trying to use a good one without ratting on my friends to the worst (as in size x badness) company I am aware of. Ohh, and I don't want to be be part of their network effect either.)