Well, they can predict the likelihood of some of that: even in the same series the Atlantic is referring to, they gave some insights: https://www.facebook.com/notes/facebook-data-science/when-lo... (Adrien, the author, is a friend, but I haven't talked about that with him).

They can, but I’m assuming (like the rest) it's neither very new (unanswered messages, asymmetric attention) or very positive, or reassuring: I remember a blog post detailing how older, more male profiles spent time on younger, more female profile a lot, especially through photos. On Valentine’s day, big corporation have a duty to smile.

On every other day of the week, the ethics of informing, or acting upon any of that seems murky at best.

+ elopements,adultery and the like.