I'll list two because I've been on HN too long today already.

1) Facebook is part of an initiative to lay down internet infrastructure in Africa, with the catch being that access to Facebook, Google, et al. is heavily subsidized. They are attempting to trap an entire continent on their platform, with subsidized tax money, knowingly simultaneously creating the most advanced social monitoring tool ever to exist. The CIA already has "social unrest" prediction mechanisms and, regardless of what some people involved think they're doing it for, this tool will be used to enslave the continent, continue preventing its people from achieving economic parity with the West, and provide better data for three-letter agencies to use in their sociopolitical and economic targeting (targeted propaganda, red herring social issues, media blackouts, even full-scale political coups)

I have not read this article but I was in a hurry to find a source to give you. I'm hoping the Guardian doesn't let me down here:
https://www.theguardian.com/world/2016/aug/01/facebook-free-...

2) They have better data than anyone else with respect to gauging addicting user behavior, and instead of taking the Nintendo approach ("Why don't you take a break and play outside?") they actively exploit these behavioral patterns to increase user engagement. 1/4 of the world's population exists on an insulating platform that does not have their interests in mind. They are unwittingly paving Facebook a permanent highway over our social systems. This creates negatively-reinforcing social vacuums and a massive chilling and normalization effect. But even worse than this normalization is the ideological reinforcement and mass hyper-emotional response that tends to result from an network of humans all checking their emotional response against others in a social vacuum. To make things even worse, Facebook capitalizes here as well and exploits users' emotional response mechanisms.

Here's a paper from a few years ago exploring this concept. I wanted to find a more recent article that was quite good but I couldn't locate it with a quick search:

http://www.pnas.org/content/111/24/8788.full

The article I wanted to find mentioned one of the ways Facebook would exploit peoples' emotions to provoke their addictive behavior:

Facebook knows John spends about 10 minutes going through his feed at a time. During work hours, this number is 3 minutes. Right when Facebook thinks John might be about to put his phone away, they will suddenly show him a post from a friend he likes. He might stick around a little longer and comment. He scrolls a little more just because he is used to the behavior, and when Facebook thinks he is about to leave again they show him a post from someone he doesn't like. Bonus points if Facebook has determined the post is positive in nature. This triggers a negative emotional response in John and he scrolls a while longer, looking for a post that will give him another dopamine rush and return his "happiness" to him.

It's disgusting. It's predatory. It's abusive. It's no different than the CIA knowingly spreading crack and fentanyl to control the population and create pockets of crime that call for increased enforcement.