The key here is the majority of the content on your Facebook feed is what your friends and family post. Your friends and family's posts have massive meaning to your life, and you will take on board their sentiment more than, say, an ad.
The meaning behind the music in a supermarket is negligible - you don't give any weight to songs played in a supermarket other than "I like this song" or "this song is annoying".
In a sense this whole fiasco is a good thing. The feed, for me, has now become less attractive as a "news source" for what my mates are up to. And that can only be a good thing. I dislike how much everyone (including myself) has taken to Facebook as a means of friends/family communication.
And this is the key issue - Facebook is not some buff actor telling you that you're inadequate if you don't buy a certain aftershave. Facebook is the lens through which people see a significant and important portion of their world. Friends, family, etc.
Artificially adjusting what is seen though that lens with the express intent of modifying someone's mood is horrifying by itself. It's even less acceptable when it is done without consent.
I'm very surprised that so many HN commenters seem to be unable to see, or unwilling to accept, this crucial and key difference.
Your analogy doesn't make sense because Verizon doesn't select which calls you receive. A phone company that drops any calls (positive or negative) is just defective. Facebook always curates what they show on your newsfeed. The neutral case where the experiment isn't being run still involves Facebook picking and choosing what to show you.
If you want an analogy relating to socializing, how about a dating site experimenting with showing you more or less attractive people? Is that terrible and unethical?
