Hacker News had various articles explaining that the EU soon will have something called the GDPR (https://www.eugdpr.org/). UK is going to exit the EU, but it's not about that in particular. If EU citizens didn't give explicit permission for this data to be shared Facebook is not following this law. As UK is questioning this behaviour it seems they'll probably have something similar to GDPR after they leave the EU.
Further, this was NOT about providing ads, instead the data personal information was shared with a third party without this being explicitly consented to. People have been profiled without this been explicit, further no consent was given. That's what is not ok.
All the other questions seem like strawmans.