I can’t agree with that. There were plenty of ways for garbage to go viral, long before the Internet. (It did take more time; I grant that much.) The Biorhythms kook, one Bernard Gittelson, managed to find a major book publisher for his work, and as it became popular it was widely written about in newspapers and magazines and covered on TV. (Not by Cronkite, but certainly by lighter feature programs and local news.) Hell, for a while respected major newspapers carried biorhythms charts.
The very paucity of media outlets gave anything which made it past their filters (not difficult) an almost guaranteed audience and faux credibility. (“There was a movie about von Daniken on NBC; he must be important!”) Again, the process took time–it was four years from when von Daniken published in German until the made-for-TV movie put him over the top in the U.S.–but the stench also lingered longer afterward.
I think what you describe is part of it, but there’s also a virulent strain of people believing that they are as qualified to interpret or evaluate this stuff as experts, and coming to the entirely wrong conclusions. And there’s also a big dose of distrust in institutions- they think the government has an agenda with climate change above and beyond the obvious.
The organic food market is a perfect example, as is climate change denialism. Both are primarily hawked by people who think they understand how things work, but really don’t. Or by people who incompletely understand something, but think they understand enough to make an informed decision.