I myself looked at my old posts and couldn’t tell whether they were private messages or not. Not that I ever used Facebook for anything truly personal.
I defend FB’s steps and mis-steps more than some folks I know, but I’d suggest that this is what happens when human ideas like “conversations” are reduced to engineering terms like “data.”
The answer to people’s fears is not to outline the different types of data they produced. It’s to clearly understand what they thought they were doing when they did it. Humans understand conversations in the context in which they were produced, and context isn’t easily reduced to fungible data classes.
There’s an upside to this, viz., Mitt Romney’s septic appeals to wealth leaking into the wider mainstream. That’s part of a general sense that local interactions have global accountability now. Sometimes that’s good.
But overall, there’s a nagging suspicion that the context for any interaction might someday be stripped from the words that composed it, and that will change how we interact. I know it’s changed me.
The perverse net result may be that we might eventually share less than we did before all this came along. And that would be sad.