[Houshalter]

I don't get the controversy over this. How is this different than a news website displaying more tragic stories or more upbeat stories on their homepage, and seeing how it affects users? Someone in another thread mentioned supermarkets playing sad music and happy music. Or even Facebook's normal newsfeed algorithm tweaking, where they've very likely done tests similar to this.

[rtpg]

Because in your example, it is an interaction between you and the news site. You expect the news corporation to do this.

Facebook is not about communication between you and Facebook, but between you and other users. Facebook is effectively manipulating communication and the relationship you have with your friends on the website.

The manipulation of the feed is subject to the intent of the manipulation. If the goal is to make sure that you see things you want to do anyways (posts by friends you interact with often, for example), then that seems reasonable. Here the manipulation is not to make the user's experience better.

[Houshalter]

Their goal is to make you stay on the website the longest, or click on the most ads, or whatever. It's not like facebook is normally benevolent and tuning their filter to help you. In any case, the filter is presumably for posts from distant friends and pages you've subscribed to, not manipulating your close friends.