I’m not sure I understand your question. With Facebook (and my example) users have already opted in to sharing that data with FB and it’s advertisers. No tracking involved.

As an aside, I think the only real problem with targeted advertising right now is that everyone is trying to do it in a covert way. Why?

Just straight up ask people what kind of ads they want to see. Relevant ads are much better than random ads, and in a lot of cases are genuinely very useful. Personally I’d happily fill out a Google “ad preference” form in great detail.