The problem is that without Facebook you will miss out. Sure, close friends and family will invite you to their social events, but more distant acquaintances will not; you know, the bloke you met at the pub last week and had a 20 minute chat with, or that cute girl you talked to but then she suddenly she was dragged off to a birthday party by her friends. By missing out on the social opportunities you lose the chance to upgrade these people from acquaintances to friends (or even lovers), as well as meet new people.
Some back story: I moved to a different country two years ago with my ex-girlfriend (for her job), and we both didn't really know anyone there. I work remote, so I don't meet a lot of people from work, either.
We broke up after a year and much to my dismay I discovered I had not really made any new friends in that year, and that I was quite ... alone. So I set out to change that. Facebook – as much as I dislike the company – was helpful. I moved to yet another country two month ago, and again Facebook has been helpful.
I dislike Facebook for all the standard reasons. I had an account but I deleted it about 5 or 6 years ago, but I decided that having a good social life was (and remains) vastly important to the quality of my life, and that Facebook is a tool to help achieve that goal.
(Facebook didn't really "delete" my old account, as after I rejoined it remembered many of my previous friends; some of whom I had no contact with outside of Facebook, like many Egyptians I was in contact with during the 2011 rebellion whom I had met through a friend and only knew through Facebook; my "suggested friends" list was full of Arabic names).
On a more deeper level, I am a little bit exasperated of always being the "different" and "difficult" person (which extends to things beyond Facebook). Standing up for your principles and "voting with your wallet" is good and all, but ... I'm not so sure it's all that effective. In this case, a more effective strategy is probably to first create a really good Facebook alternative (I'm not so sure there is one now), make sure decent privacy laws are enacted, etc.