Google/Facebook don't have to sell your info to advertisers because the are advertisers. Either way it is used for commercial advantage.
a) You need a credit card, excluding large chunks of the world population that doesn't have one
b) Google/FB learn your real identity via the payment networks, verified to banking level
I get that advertising is annoying. Regardless, painting it as some kind of scary privacy problem doesn't make sense and worse, muddies the water. People end up dumping tech companies into the same boat as governments even though they have hardly anything in common.
One project I've been meaning to delve into is https://sandstorm.io/
On your last point; Tech companies and governments get put in the same boat for good reason- they actively work together on a regular basis. Even if the company is "compelled" to give the info- that's still only an issue because the companies are whoring and storing all the data they can get their hands on (for indefinite amounts of time).
That's pretty damned creepy.
For instance, Facebook lets advertisers show ads to users of age X, working at company Y, in location Z, etc. (without disclosing their identities). This is completely different from selling your information, and the companies' privacy policies and practices reflect this.
As mike_hearn says, these sorts of alarmist claims ("they're selling your info!") are easily debunked. And in this case they detract from the rest of Julian's essay, which is a shame because elsewhere he makes some good points.