It's also the most overlooked. It's good to protest the other mechanisms of authoritarian control, but propaganda is enemy number one.
You don't need the ability to spy on dissident groups if you can control public thought enough to prevent those groups from forming in the first place. You don't need the ability to quash public uprisings if you can propagandize people away from rising up at all. And they can. And they do.
The ability of the plutocratic class to manipulate public thought at mass scale is the single most overlooked and under-appreciated aspect of our society. It warps the entirety of our political spectrum, all our thinking, all our discourse, and what we perceive as normal. And you just don't see people fighting it. The ACLU isn't protecting people's mental sovereignty from the manipulations of sociopathic government-aligned oligarchs. People aren't taking the media-owning class to the Supreme Court for brazen election interference. People aren't taking to the streets protesting it. But they could.
In terms of the effect it has on society, no control tool comes remotely close to advancing as many interests of the powerful against the interests of the people as domestic plutocrat-sponsored propaganda. Nothing will change until people start noticing and resisting this.