It's not about the things we put on facebook anymore, and it's not about the things our friends put there anymore either. Now facebook collects data about any site I may visit, see
this article describing the problem, a "bug" facebook "fixed" already, (my guess is they just hid it from the users). This happened to me the other day.
I don't like a centralized place where my browsing info is stored, and where all my family and contacts can be related to that info. I'm not interested in anyone knowing that me, with parents named such and such, that attended school such and such, etc, just browsed a hentai porn site.