It's all the external feeds wanting your attention & commenters throwing in their 2 bits that are the random noise. This is the domain where the propagandists are working, and where there is no and should be no trust. There's no difference between some nobody posting from their personal account, and some nobody posting from their account that they've slapped a logo on. There's no distinguishable difference between 100 nobodies throwing in their heartfelt opinion, and 100 bots repeating the opinion of 1 nobody.
Your new position is still too extreme; human trust is not binary. We could go another round where I point out exceptions and you come up with another model that is still too simple. And again, and again. Eventually, we might even get to a point where a useful discussion could be had. But it's not my job to force you to think past your taste for dramatic statements. It's yours.
If Facebook and Twitter were no more useful or trustworthy than 4chan, then they wouldn't exist. It's like saying, "I can't believe people are trusting encyclopedias and cookbooks. There's no reason that readers should consider them any different than stuff written on a bathroom wall."
The problem is the gap between what they sell themselves as and what the actual user experience is. If Facebook were advertising themselves as the cloaca of the Internet, your vigorous user-blaming would have some merit. But they don't. They aim to be in daily use by every person in the world, a trusted intermediary. They either need to live up to that or quit.