So the reason why Americans shouldn't use Facebook is because it's possible that some rogue government somewhere might oppress its people? Those governments seem to be doing a pretty good job already without Facebook's help.
Then there's the argument that in 30 years the US will be one of these countries, too. I wonder why people are so afraid of this, but not of the small chance that they'll be hit by a meteor when they go outside tomorrow to go to work. They've been hit by a meteor exactly as many times as their government has used a "social graph" to oppress them, after all.
For most of human history most people in the world lived under tyranny. In that light the freedoms we enjoy in the USA are a pretty small blip in the data. Why do we think it will always be so, especially with so many people apparently unconcerned about the unprecedented ability of both commercial and government organizations to accurately profile the public/citizens?
That's just one obvious example. As for your analogy, that's like saying people were already doing a great job communicating via phone and email, what's the point of IM, twitter, or social networks in general?
You're vastly underestimating the potential value of access and storage of more and more precise behavioral data combined with the innovation of a startup vs the stodgy, uncreative, stubborn ways of both old world telecom and finance corporations. Back then, even with access to people's purchasing data and past addresses, I would have had to do a lot more work and ask for larger increases to our budget to figure out people's relationships as well as non-purchasing behavioral data aside from traffic. Now I can potentially have access to people's preferences to stuff as opposed to just guessing. Today it's much easier and cheaper.