Facebook's Tools can Target a Single User

Well I would think the title above is clearly true, but the question is how effective is it in a useful context? And is that ethically more powerful than a typical ad?  

Researchers Show Facebook's Ad Tools Can Target Single Users

TechCrunch, Natasha Lomas, October 15, 2021

Spanish and Austrian researchers have showed that Facebook can target ads to a single individual, given sufficient knowledge of that person’s assigned interests. The researchers described a data-driven model that characterizes a metric indicating the likelihood a Facebook user can be identified based on interests attached to them by the social media giant's ad platform. The model found that "the four rarest interests or 22 random interests from the interests set FB assigns to a user make them unique on FB with a 90% probability," the researchers wrote. These findings raise issues about potentially harmful uses of Facebook's ad-targeting tools, and about the legality of the platform's personal data processing system. ...