Can you provide an example of facebook "selling private data"? I work there, and it would be a great surprise to me if you could.
http://en.wikipedia.org/wiki/Facebook#Beacon
The prime example that resulted in a lawsuit settlement. I mean really? Opt-in to reveal your purchasing and browsing habits with selected companies and then spam your friends?
http://gawker.com/5426176/facebooks-great-betrayal
Another opt-in that is equivalent to Facebook buying web coverage at the expense of user privacy.
http://gigaom.com/2010/04/22/facebooks-instant-personalizati...
These websites are able to scrape your data to provide you a "personal" experience. Another opt-in. I'm not sure if FB is selling this api, but I'm willing to bet its a certainty.
These might not literally be bundling up personal information and selling it outright, but given the track record here, I wouldn't be surprised if they did another "opt-in".
None of these programs involved facebook giving user data to advertisers. Even the dreaded Beacon was strictly one-way: it allowed sites elsewhere on the Web to publish to facebook, not vice versa.
Out of curiosity, do you hold Google's AdSense up to similar levels of scrutiny? You're aware that a little pixel is on about 70% of the web by hits, piping your interests, proclivities, and browsing history to Google advertisers can target you? Or is it not evil when Google does it?
Your argument is analogous to saying Microsoft didn't really have a monopoly because 3% of computers used Linux and OSX. Plus, how does F8 instant personalization work? I doubt it is solely based on a 1 pixel tracking image.
And I do hold up AdSense to the same level of scrutiny. While it also has privacy issues, it is not of the same level. It does not force browsers to become advertisers to their friends, revealing their purchasing and browsing habits. Your friends do not know that you visited a certain website or bought a certain product and can link you by your name, age, friends, and likes/dislikes and organizations you belong to.
That is the sole reason why people think Facebook can beat Google.
You want to make some sort create some sort of moral equivalence between literally selling user data and changing user privacy defaults. Maybe there is some moral equivalent, but I don't think so.
In any case, the way you made your case is by lying. An anti-US activist might want to claim a moral equivalence between the casualties of the Iraq war and mass executions. But, to say that the US executed 100k Iraqis is lying. That is an analogous to your argument.
A more apt analogy using your theme would be this: Saddam Hussein didn't kill anyone, his soldiers did. Only a pedant would be worried about the literal meaning without looking at the big picture.