How does it affect passers by? — frank
Maybe a good "natural experiment" on this is to look at attitudes towards climate change. It's
A
(1a) settled that anthropogenic climate change is real
(2a) settled that the differences arising in the climate from our actions are relatively large
(3a) settled that we're already feeling these effects in social problems and extreme weather rates
But in discussions about it you see:
B
(1b) Attempts to discredit the sheer mountain of evidence of the reality of anthropogenic climate change by focussing on single (usually misattributed) study flaws or counter-variation (like the El Nino cycle) or erroneous claims.
(2b and 3b) Attempts to discredit claims that the difference caused by humans on the climate is large by focussing on "so it's an apocalypse now eh? What about the Mayans and the Millenium Bug!" like claims; false equivocations and hyperbole, then denying it's hyperbole. Looking at information in a highly decontextualised manner ("This part of the Greenland ice sheet has been growing this year!") to refute a well established general claim. "Who cares if this island people have lost most of their land from sea level rises? It's an isolated case!" (ignoring literature on climate refugees)
If you imagine an observer coming into a social media discussion, they'll see supporters of settled science A speaking on a level playing field with supporters of lobbying derived bullshit B. Usually what's happened appears to be a clickbait article about climate change has a bunch of falsehoods in it, skeptical individuals will realise that the article is clickbait and remain unconvinced, but precisely the same thing holds for reporting on well researched science.
Part of the effect is to create, as you put it, a fog where people can't tell true from false
because they are equally skeptical of all claims. In a situation where someone's belief is not driven by contact with well reasoned argument and evidence, emotional and discursive factors play a bigger part in informing and maintaining belief; what's true becomes little more than what is presumed in what media you expose yourself to.
Another part of the effect relates to derailing - or controlling the conversation - making claims that lure people into responding and thus increasing the "broadcast strength"of the original message if the responses explicitly correct it and react to it rather than providing their own narrative. Even if everyone who responds to it disagrees with it. The "lure" works by exposing skeptical or hitherto unexposed people to a claim, or a framing context for a claim, in a situation of heated debate; so when you just "skim over it", you see good points from both sides, but one person (like
@NOS4A2) is controlling the flow of conversation - what topics get brought up in what way, and what easy refutations there are for them. It's to the benefit of a position's exposure to be obviously wrong or implausible given an informed perspective and divisive between people who are uninformed (read: skeptical in the usual "the news is so biased now" sense) on a matter; that's good misinformation, it makes waves, it goes viral, it frames discourse, it creates bottlenecks of inquiry through saturation (want to know about X? well guess what, it's similar to Y on the internet - now you know about Y).
The major distinguishing feature, I think, between intentional misinformation and just being misinformed is that intentional misinformation about X is designed to intervene on how the discourse surrounding X works, not to work within it to assess and challenge claims. Being dispassionately reasonable about an issue when engaging someone who is intentionally misinforming can still help them saturate the medium with their message, or the presumptions underlying it.
The role that presumptions play is easier to see in talking about trans issues, a recent popular issue was "should trans women be allowed to compete in women's sports?"; which is a neatly packaged clusterfuck overlapping the question of the distinction of natal sex and gender, the possible effects of bodily differences between trans women and cis women, and sports fairness intuitions. Misinformation is designed to make waves and push the exposed into a desired position; through divisive or occlusive framing, through taking a lot longer to correct than to state, and to appeal to the ultimately aesthetic and heuristic components of belief formation than the logical or analytic ones.