How exactly would my lack of privacy weaken anyone else's privacy? Is this just a generic slippery-slope argument? What is the causal mechanism that would cause my lack of privacy to effect anyone else's?
The network effects of popular but privacy invading platforms are what allows the lack of privacy to spread. If you use Facebook, as an example, then everyone else who uses Facebook in order to interact with you, or anyone whose face is included in a Facebook photo by you has their privacy affected by extension. Someone who's not even on Facebook but just happens to know you now has a shadow profile and their biometric data indexed somewhere in Facebook's database.
> The network effects of popular but privacy invading platforms are what allows the lack of privacy to spread.
That's just a bunch of handwaving. Be specific about causality. "Network effects" is pretty much equivalent to "stuff just happens for some reason."
> Someone who's not even on Facebook but just happens to know you now has a shadow profile and their biometric data indexed somewhere in Facebook's database.
I don't believe that for a second. That's a wild accusation made with no evidence.
It's not unreasonable to assume that they build shadow profiles on every potential subject they can identify and can begin to graph relationships from, including every face they can isolate from a photograph, even if those faces don't belong to Facebook account holders.