Thinking back, we considered a "Sad" reaction but were concerned that some might use it to mean "Pathetic" rather than "it makes me sad". "Unhappy" could mean you are unhappy with the poster rather than the news or information. The right tooltip is as or more important than the icon.
It is important to be very careful and take time to look at this from different perspectives. Aside from the English language using the same word to mean many different things, not everyone is a native English speaker. We can't change or delete a Reaction once introduced without making a huge mess.
Also, remember to up or downvote this suggestion to help us gauge the interest.