If I was well-assured that if I participated in Facebook all of my posts, private messages, likes, etc. were truly private and would never ever be released to the gov't or any other entity in any way, ever, under no condition such that they could prove to be self-incriminating, I would use Facebook. But I know that isn't the case, and hasn't been the case for a long time, and thus I don't use Facebook nor have I ever.
There are a lot of millennials who plainly did not realize this. Whether it was willful ignorance or whatever else, I don't know, but I can tell you that a good bunch of them now are not happy that this is so. They just feel powerless in being able to change or challenge the status quo, which I guess they actually are. They could stop using Facebook, but that decision comes at the expense of losing out in other important parts of life.