Isn't this the case already? I expect every post I see in large social media sites posted by somebody I don't personally know to be non-organic feedback by a social media expert.
People are doomsaying over a scenario that's identical to the present world.
At that point, social media will probably split into hyper-local services for people who know each other personally, and an enormous amount of AI-powered rabbit holes for unwary (or depressed, lonely, etc.) users to fall into.
Maybe I am too pessimistic and we will be able to fulfill everyone's needs one day. But as the rich keep getting richer and focusing on power for themselves that doesn't seem like a direction that we are going to move towards soon.
Second, I think you are being too pessimistic. In the sense that you feel like it isn't a solvable problem. I feel like people have thrown their hands up on this problem because in the history of the internet we have not been able to solve it. For me that just looks like a conclusion drawn from insufficient data. To me modern internet is quite young in the grand scheme of things. We haven't even had a generation live out their full life all online. I think we at least should have a hopeful tone about this problem and encourage people to work on it. Presently it feels like everyone is in doom mode.
I don't feel like this is specific to the internet. People have been scamming other people for thousands of years. Sure, the internet makes it easier to extend a scammers reach and easier to get away but the fundamental concept is unchanged. Maybe it is a solvable problem, that would be great. But it also seems like this is unlikely to change soon, so at least in the meantime we need to remind ourselves to be careful who we trust.