Facebook is a tool. What you choose to make of it us entirely up to you. It can be useful for socializing, reconnecting, staying connecting, staying informed, and so on.
It can also be a tool used to turn you INTO a tool. Think the proliferation of "selfies" and "selfie sticks".
As for data harvesting? Yeah I'm sure they do it. But so what? You think they are the only place that does it? Even if you hate the online world, adamantly refuse to get an account, and "stay off the radar as much as possible", you would be aghast to learn how quickly anyone can learn a lot about you.
They key to all this seems to be using a little common sense (I know...a lot of people don't) and understanding that it pays to be picky with what you choose to "like", "share", comment on, and add as a "friend'. I almost always ignore and block game requests, most lowbrow memes, and anything that urges me to 'like' and 'share'. Also by posting multiplicity of interests, including random stuff from left field, it makes it difficult for the data mining algorithms to get an accurate read on you.
And learn how to use your privacy settings.