However, they need to pass two other tests, a "necessity" test that determines that the processing of information is necessary to serve the interest, and, most crucially, a "balancing" test which balances the commercial interest against the user's interests, rights, and freedoms. It's this latter part where more onerous advertising practices will falter.
https://ico.org.uk/for-organisations/guide-to-the-general-da...
Also, does Facebook's ad network really constitute "direct marketing"? I had imagined that to be more of an email blast about a new FB feature, rather than collect-your-usage-data-and-sell-marketing-slots-to-you.
Now that I type that out, I guess it does make more sense. However, I really am not a big fan of the common-law approach to the "balancing" test. Basically, whoever has the most money and faces the most lenient judge wins. Everyone else is left guessing what the hell is legal and what isn't, when a clear set of rules would be much easier to fairly apply to everyone.
Vote me down all you like, but it doesn't affect what is actual legal fact :-)
It would be interesting to see revenue as a necessity be tested in court, since there are open-source social networks that don't rely on user tracking or data sales to the extent that Facebook does it.