Is this correct? There was a very involved discussion about WhatsApp's encryption that I thought indicated they don't, in fact, have access to WhatsApp messages.
Suffice it to say: (Paraphrasing Dijkstra) Whether Facebook understands human emotions from text is as relevant a question as whether a submarine can swim. I think they can get a helluva lot out of what you're typing and what you're liking. That should be enough to worry about.
But lexical content is a very well understood field, and emotion recognition is a huge industry for advertising. Even if facebook doesn't know that "I like it when stan fingers my butthole" was just a joke between buddies... there is tone inferred from the words and grammar involved. Positive vs. Negative is relatively straightforward, and when associated with a topic... can lead to lots of "opinion" data.