This is very common on HN these days - stating something with a lot of confidence that turns out to be some self-constructed mental model that has nothing to do with reality. Then, add the obligatory "all related studies are showing it" and you have met the publishing standards.
Legally or illegally, morally or immorally, for better or worse, Facebook has created the most sophisticated ad targeting engine the world has ever seen. You want proof? Look at their financial statements. You want more proof? Look at all the companies that went public on the back of Facebook's ad targeting engine. Again, perhaps it shouldn't exist in the first place, but trust me, it works.