When you say Facebook is "selling data", I think most people would understand it to mean that advertisers can go to Facebook and buy a list of people who eat at McDonalds. That's very different from the opaque ad targeting Facebook actually sells.
There is a connection between the ad targeting information and the eventual anonymous click through though. You only need to connect that click to a real identity via either self disclosure (newsletter signup, social login, etc) or pushing your metadata through third party data brokers.
In the end you have a click associated with an advertising campaign linked to a real life (or even pseudo) identity.
Are you implying that this is a problem that arises specifically from Facebook's targeted advertising? I genuinely don't think that's the case.
It doesn't really matter if ads are served to everyone or if they are shown only to a targeted demographic - either way, only people who are interested will click on them. Also, I think it is safe to say that, roughly, it is only the efficiency of clicks per ad-view that will increase if one uses targeted advertising.
So, if the act of clicking a targeted advertisement does not in itself somehow "transfer" any more identifying data than a click on a regular ad would, which I don't think it does, then what's the problem?
Facebook is incentivised to collect and collate product data because it can then sell targeted ads for those humans. As long as the most cost effective path to those targets is through Facebook, and the aggregate target volume is high enough they will make money. Distributing the login data is just advertising.
That argument goes both ways: When you say Facebook is "selling ads", I think most people would understand it to mean that advertisers can buy ads like in a paper magazine. That's very different from the tracking and targeting ads Facebook actually sells.
“Hey, I heard you’re opening a baby store. Did you know John and Mary are expecting? Here’s their phone number, you should call them up.” vs. “Hey, I heard you’re opening a baby store. If I know anyone who is expecting I can let them know.”
Signals. Searching for specific things, emails you're receiving in Gmail, videos you watch online etc.
Given Target was able to figure out someone was expecting based on behavior in their store, back in 2011 [1], even though they dont have a loyalty program, imagine what can be done with so many trackers that are on the web datamining your behavior from one website to another.
It's important to remember, because someone might propose a law against a social network selling data. It could be heralded as finally giving users privacy. And Zuckerberg will be very happy that this PR mess has gone away