Bloomberg:

It’s a way of creating a connection, even if it’s superficial. If users click like on a post about the Red Cross’s disaster relief efforts, they feel as if they’ve done something to help. (In January, Sandberg went so far as to suggest that likes could help defeat Islamic State: By posting positive messages on the terror group’s Facebook pages, users could somehow drown out the hate.) Liking someone’s photo is an awkwardness-free way to make contact with someone you haven’t seen in years. Alternatives to like will let Facebook users be a little more thoughtful, or at least seem to be, without having to try very hard.

I think that “without trying too hard” is the sad key to the Like button. Regardless, the article is an interesting look behind the scenes at Facebook and the massive amount of discussion and thought that goes into something seemingly so simple and obvious.