It baffles me, too.
I have no doubt that if used properly and to one's own advantage, Facebook can be an awesome tool for many things. However, there have been a couple of well-publicized downsides. Off the top of my head:
1. I've heard stories of job offers being rescinded because of behavior witnessed on Facebook accounts.
2. Kids often post pics on Facebooks that have been taken using smartphones. Last year, it was discovered that such pics contain GPS technology embedded in them. Predators have been using this technology to actively stalk children. As a father of two teenagers, this is the one I have the biggest problem with.
Hopefully, I've helped you guys to become a little more unbaffled.
1. Well, yes, one is responsible for what one says or does on the internet. FB has nothing to do with it. One can find out a great deal about a person by reading posts on Organissimo as well. And if privacy settings are set up properly, only those who you allow to see anything you post can, well, see whatever you post.
2. Again, GPS info is more a feature of smart phones than of FB itself - and can easily be disabled on both platforms. Given that FB has something like a billion active users, I also doubt your fears are as widespread as you might think. Again, if privacy settings are set up properly, there's no way a "predator" could even see your postings - unless you let them of course.