I got off of Facebook after being on for 6 months back in 2011. I left for a few reasons:
1) It was an unnatural social for me. IRL people from my past like high school and college--that I let go of-- aren't walking up to my door and asking if we can friends. If that did happen, I would ruminate over every decision to be friends. I'd worry over it. It'd be overwhelming. Well, the same on Facebook for me. I worried about rejecting people. The day I deleted Facebook from my life was the day I asked myself "what are you doing on this platform anyway?"
2) Facebook kept changing my privacy settings without warning. I continuously had to go in and opt out (after months of not noticing they changed). More than a few users lost friends and jobs because of these unannounced changes.
3) The constant political and religious posts coming from people.
4) People trashing their spouses publicly during divorce battles
5) People posting pictures of their children. I find this to be a stupid, unnatural, unprotective thing for a parent to do. It equates to my mother taking all the pictures of our family and handing out copies to everyone at work, the church, and a bunch of strangers in the street. Do you really know that guy from high school that you haven't seen in 20 years that you added to your friend list?
6) Lastly, I realized what Facebook was: a data-collecting scheme connected to your real identity. Facebook is forming psychological profiles from private chats, information given freely, searches, how you play games, who you're closely connected to out of your group of FB friends and what you share with them "privately" on FB. They have what you look like from all the photos you provide. They perform psychological experiments on users without permission. And so much more.
That's why I got off. I've never looked back. If I'm interested in a topic, I can find a sub on Reddit or some other message board. I keep in touch with people who are actually my real friends and family through email, phone, and text. I have no fear of missing out, and rarely do in terms of events with family and friends.
Still, I want people to enjoy Facebook if they like being on there. It's their freedom, their lives. I have no agenda to make them delete it.