Danah Boyd thinks deeply about Facebook emotion experiment: What does the Facebook experiment teach us? Here’s a bit of it:
Somehow, shrugging our shoulders and saying that we promoted content because it was popular is acceptable because those actors don’t voice that their intention is to manipulate your emotions so that you keep viewing their reporting and advertisements. And it’s also acceptable to manipulate people for advertising because that’s just business. But when researchers admit that they’re trying to learn if they can manipulate people’s emotions, they’re shunned. What this suggests is that the practice is acceptable, but admitting the intention and being transparent about the process is not.
There’s even better stuff further on, and you should read the post.