I realize that Facebook is basically a data-mining corporation, and that there is little to no privacy, but as others have pointed out - correctly, I think - in general, and ESPECIALLY if anyone's had an online presence, which I have since, I guess, 1997-ish, my privacy was compromised a long, long time ago.
I do realize that it can be a cesspool of negativity and time wasting. My one experience with Facebook was 2010-ish, when a cousin I was visiting said "Hey, do you want to check out my account" - she let me sit at her computer and browse around. I thought I'd be on there five, maybe ten minutes, and be done; next thing I knew, three hours had blown by (she and I grew up together and knew/know a lot of the same people, so I kept seeing familiar faces in her friend list, clicking on 'em, etc.)
I'm far from sold (especially since creating this thread) on the notion of signing up, but I don't think the "invasion of privacy" argument holds a ton of weight, given that I've been online since the late 1990s. And I'd be very vigilant RE: not getting involved in, well, almost anything, ha ha; as I have said, IF I sign on, it will mainly be for networking, marketplace, and keeping in touch with a select few family and friends.