You argument is basically a milder analog of "Humans die from all kinds of causes so let us let murderers walk free."
This is no different than a television series like I mentioned earlier. You can argue you want the raw footage from a reality television show, and not the heavily edited version designed to manipulate your emotions, but that's not your choice.
They seem to be following those terms, they were choosing positive and negative stories for feeds, and then analyzing the data to see if users then posted more positive or negative posts in return.
1. '...we may make friend suggestions, pick stories for your News Feed, or suggest people to tag in photos...'
2. 'The News Feed algorithm uses several factors to determine top stories...'
3. 'How we use the information we receive... for internal operations, including troubleshooting, data analysis, testing, research and service improvement.'
You did not answer my other question. Here is a more direct question.
Should Facebook be exempt from laws on human experimentation?
Facebook should obviously be bound to the same laws as everyone else. Which human experimentation laws did they break? Users registered on Facebook and agreed to the terms of service, and how Facebook will choose which stories they view, and analyze their response.
I'd think Facebook has even less control, and more difficultly predicting emotions. For example, if Facebook displays a post about Jane having a bad day and losing her job, that's bad news. However, it's difficult to determine how I'll react. It might be comforting for me to know someone else is having a bad day, it might make me angry that Jane lost her job, when I lost my job at the same business the week prior, it might make me happy because Jane is always bragging about her job, and I no longer have to hear about it.
When it comes to a movie, I think there's a lot more control since you write the script and characters from start to finish. Every person in the audience has the same relationship with those characters, and knows them for their entirety. You also have fine grain control over the visuals, combined with carefully selected music. As I said earlier, all of this can lead to a room full of people leaving the theater in tears, so I don't see the difference.
Or, when you say we do at our own will, you mean we make the choice to visit the theater in the first place? That would be no different than making the choice to visit Facebook. If anything, you should be questioning every advertising campaign in existence. They're carefully crafted to evoke a certain emotion, and they work specifically because they can manipulate people. At the same time, people have no choice to view them, they're constantly exposed to these manipulations just by walking outdoors or visiting the store to buy groceries.