Overly engaging social media has weaponized conservative news media, among many other things.
Blasting propaganda over cable, radio, magazines and such is as old as America itself. Thats fine. Its part of the deal. But a device that lives in your pocket, essentially required for participating in society, with many billions spent on stopping you from disengaging is an entirely different thing. There is no good historical precedent for how psycologically manipulative that is.
Its unacceptable because China could quite probably start a civil war with such influence. Its not OK for Facebook, Google, or any government to have that unchecked power even if they just use it to sell ads or whatever.
So... I dunno where the line should be. But wherever that is, we are well past it.