Earlier quoted context omitted.
What if your service requires the tracking?
Consent isn't required for data collection that is necessary for the service to work. However, you have to be prepared to defend in court that it IS necessary. As such, trackers in 3rd-party advertising network code probably won't count as necessary; it's necessary for the ad network, but it is not necessary for the website displaying the advertisements, as proven by ad-blockers. Likewise, the facebook like button an…
I'm pretty sure Facebook has the resources to have hired competent lawyers to advise them on that, and the money to afford preparation and execution of a strong court presentation of their viewpoint.
And Facebook probably had more information on what is necessary for the system Facebook provides to work than people trying to guess that from the outside.
It is, of course, possible, and, perhaps even likely, that a court will disagree with what they argue, and force a change—but it may be, from a PR perspective, worth the cost of non-compliance sanctions to have any decrease in utility resulting from changes they will be compelled to make to be very visibly forced on them by orders that they vigorously fought rather than self-initiated, so that European authorities and the GDPR get the blame for any reduced quality.