You don't seem to understand that one can do behavioral tracking without sharing all personal data with Facebook and Google. GDPR is mainly focused on who you share the data with. Performance tracking of core business processess including traffic sources can be done without involvement of Facebook and Google.

It's totally legit to spend a career helping the folks at Facebook and Google to soak up more private information about everyone so the Trump campaign can improve targeting of the fake news advertisements for the presidential election campaigns. But it is not ethical.