Earlier quoted context omitted.
Your hypothetical evil government isn’t going to go “aw shucks, I guess I can’t kill the unbelievers because Facebook doesn’t track them!” Evil regimes have never had a problem finding lots and lots of citizens to kill in the 99% of human history before the internet.
Big data aggregation makes this process much much easier. We are living in unprecedented times of mass surveillance, and we have yet to have a real reckoning of what that means in the hands of extreme ideologies. Also things don't have to be as extreme as literally killing all members of a minority group for this to be deemed "bad". It can be as simple as targetted influence campaigns to push certain policies/agenda.…
Advertising in Inc vs Wall St Journal vs People magazine vs Wired vs TV Guide vs Car & Driver vs Cosmo vs Ebony all gave you easy ways to target different audiences. It's more targeted now, but I don't think it's multiple orders of magnitude more powerful (mostly because the reach isn't nearly the entire story; you still have to influence after reaching.)