To ensure Messenger's machine learning features continue to grow and adapt (e.g., smart replies), Facebook needs access to users' messages. Encryption obviously gets in the way of this mission since it prevents Facebook from intercepting and analyzing those texts, hence the need for users to opt-in. It's the same stance Google's taking with its own smart messaging app, Allo -- another platform that offers optional encryption.

The move underscores growing concerns over privacy and digital convenience. For users, however, it presents a dilemma -- if you want the sort of lazy, machine-assisted service provided by the likes of Google and Facebook, you have to be willing to let your privacy guards down. If you value privacy, then you have to be content looking in from the outside.