The trick is that the legal ground is not based on consent but on performance of a contract, in which case consent, freely given or not, is not required at all.
I understand the trick, I just don't believe that it can play out.
A contract also needs consent. This contract is clearly entered only because Facebook is making it a condition of using the service, and this type of coupling is prohibited.
> This contract is clearly entered only because Facebook is making it a condition of using the service
The contract is entered when a user registers at Facebook. However Facebook seems disagree about what the contract involves. Any sane person (well, 96% of them, as the article claims) would say that the contract is for delivery of means to communicate with other people; Facebook seems to argue that the contract is for delivery of personalized ads.
A contract also needs consent. This contract is clearly entered only because Facebook is making it a condition of using the service, and this type of coupling is prohibited.