Except that in some instances, the areas where these posts are being made are in what the posters deem to be a closed room, and I'm sure you'd be mad as hell if your comments in private are purposely eavesdropped.
Obviously there is a lack of control over this by most users, and maybe their understanding of the tech they're using is limited, but by posting something on a wall in facebook and thinking that only their friends can see it because those are their privacy settings does make it private to them.
I tend to take your advice for most things, but still, it's stifling to live constantly thinking about whether you can safely voice your opinion. And in my opinion, that is not exactly a free society, either.