You remember how you feel when you use a product. When I comment on HN I feel like I'm standing before a military tribunal that is trying to pick apart everything I say and find a way to disagree with it. When I use Facebook I feel nothing but love and appreciation from the people I know and care about.
You may think that's lame or that you're above that, but I deal with enough shit in the rest of my life that I don't mind having a cushy place online to communicate with the people who care about me. And I'll even put up with Buzzfeed and email-forward-worthy garbage to do so.
On a macro scale I think that's something the world needs badly. I think most people could do with a little more love and positivity in their lives.
We're totally not.
So, I think it still merely proves the point being made above it, regardless of its supposed intent to be funny at someone's expense.
The purpose of reactions is to provide an alternative for people who don't want to click "Like" on stories of tragedy (e.g. someone's loved one dying, someone announcing they have cancer, or even something non-personal like a news article about a mass shooting) because it sounds inappropriate, like "ha ha, I'm enjoying your tragedy!". There are two reasons why this is important:
1. Some people want to exhibit support but don't know what to say, so they're not comfortable commenting. On more positive stories, they'll just hit "Like", but that would feel inappropriate to do on a more negative story, so they don't do anything even though they want to express their support.
2. Facebook's News Feed algorithm uses Likes to determine how articles are sorted in your News Feed. If people don't Like important stories because they feel the word "Like" is inappropriate, then those stories will be downranked because the algorithm doesn't know the stories are supposed to be important.
Reactions solve both by allowing people to both wordlessly express sympathy for and signal-boost stories that they feel would be inappropriate to "Like".
That's not the semantics of the Like button however. The Like button's semantics, as used by most people, are "I have read your post, don't have anything meaningful to add, and agree with you and/or express my post-appropriate social action but do not feel affected enough or close enough to you on the social graph to leave a comment."
The meaning of a Like is extremely contextual. And most people know this.
Granted, a lot of newbie users get confused.