Yeah, OK, now think about the version Facebook (and thus law enforcement, intelligence agencies and advertisers) has access to.
To be concrete, my local supermarket and Amazon have my full name, and partial purchase information (the supermarket via a loyalty card). Both have ways to contact me with promotions. You don't think they'd like to know what I like on Facebook (if I did that) or what I search on Google that might suggest purchase intent?
I think they'd love that data, the platforms just make more money by only allowing them to target with it.
The only difference that I imagine exists is being able to search from the pool of "everyone" rather than "your friends", but that would make it less confident. In the law enforcement version, there would probably be a way to anchor the search to another individual just to improve accuracy to an acceptable level.