I have a few a"friends" that post horrible stuff. Conspiracy theories, rants, and other posts that are just symptoms of poor mental health.
At first I stopped to read these in HORROR and disgust, because they stood out so much from the rest of my feed. Facebook takes that as a signal that this is the content I enjoy, and begins to feature it more and more heavily.
Looking back, if I had understood what was happening, I could have used Facebook correctly and worked WITH the algorithm. You have to think about the long term consequences of your viewing activity, and think of using your attention like farming to grow a good feed.
Facebook eventually needs to introduce a self-curation tool, so that people can promote the things/people they want, and remove the elements they dislike without Unfriending Grandma. For me it's probably to late. At 34 the college friends that I would like to keep up with haven't interacted with me in 5+ years, and the social awkwardness of rekindling those relationships isn't worth it.
On an unrelated note, I think many social networks will continue to die this way. As people move from PEAK FRIENDS in colleges to having lives where immediate family takes priority, I think the social presence will fade. The networks will take the blame, like MYSPACE, and FRIENDSHIP just are not good tools anymore, when really it was the person who went from having 100+ active relationships to 20.