Facebook likely has a watson-like technology that can answer a lot of interesting questions about a user, but "understanding emotions"... that's still a ways off. Maybe a long long way off. But it's wrong not to be very, very concerned.

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.

Author here - you're right. I've made an edit accordingly. Thanks!

Wasn't there a case of FB doing some kind or research where they tried to influence the mood of the users by manipulating what content they see?

"Understanding" emotion is definitely a biological trait that computers are unlikely (maybe 2200) to ever be capable of replicating.

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.

Unless Facebook has some sentiment analysis tech that's far better than academia's (which isn't that unlikely), "understanding the emotions" of statuses is still a long way off.

they could bake a pre-trained CNN into the messenger pretty easily and run it locally... so plausible

It is impossible for FB to understand that.