Can you link to source for this (the part that says you can't deny access)?
> When assessing whether consent is freely given, utmost account shall be taken of whether, inter alia, the performance of a contract, including the provision of a service, is conditional on consent to the processing of personal data that is not necessary for the performance of that contract.
It somehow says a whole lot and not much at the same time. Since every member state and everyone who has to comply needs to interpret what GDPR means there are various “recitals” that offer official guidance. One of those is Recital 42 - Burden of Proof and Requirements for Consent[1] which says:
> Consent should not be regarded as freely given if the data subject has no genuine or free choice or is unable to refuse or withdraw consent without detriment.
So a person must be able to refuse consent “without detriment” and the company is meant to provide an equivalent, but necessarily identical, service to those who do not consent.
What that means exactly is, of course, the subject of much litigation. For example is it a “detriment” to require a subscription fee to those who do not consent to information sharing? So far one ruling (Austria) has said no, provided the fee is reasonable while another (UK) has said yes, the equivalent service must also be free.
As far as how the coupling prohibition should or will apply to a company like facebook - where harvesting user data is the entire business model - I think that is yet to be clearly determined. As are most of the nuances and technicalities in GDPR.
Edit: I should also note that consent is just one avenue to legally allow a company to process user data under GDPR. It’s not the only avenue.