alt Hacker NewsPropaganda *also* works when it's the main source of information. This can be done in many ways.
One way is simple repetition of the exact same thing: https://en.wikipedia.org/wiki/Illusory_truth_effect
Another is to have many different lies: https://en.wikipedia.org/wiki/Flood_the_zone and https://en.wikipedia.org/wiki/Firehose_of_falsehood
Taking a step back, there is another way for propaganda to function that doesn't even require being the main source, but simply to make the lie so huge that people can't process the idea someone would be *that* level of dishonest: https://en.wikipedia.org/wiki/Big_lie
Consider your own previous comment:
> you get one half truth from one source, another half truth from another source, then two halves make whole truth.
What happens when one source says that the Alpha Party* consists of child-eating devil-worshiping lizards from Alpha Ceti 5 who caused the 9/11 attacks to cover up how the mind-control chemtrail fluid they were making in the WTC burned hot enough to melt steel beams, and the other source says the Alpha Party is standing on a platform of reducing the tax burden on hard-working families?
The latter can be a half-truth, but you don't get even a little closer to a full truth by adding any part of the "other side".
* A made-up party, any similarities to actual persons is coincidence and all the usual disclaimer.
Your links give examples of campaigns that happened, but didn't quite work. You think the problem is their very happening? And the very fact that you know about child-eating devil-worshiping lizards from Alpha Ceti 5 shows that an opinion is available no matter what propaganda you use against it as long as it's not censored. You can suppress it only by censorship, not by propaganda. In any case using shitposting sites as a source of information is tricky, journalism isn't that bad yet.