It used to be that every village has an idiot. And everyone in the village knew who that was. They’d talk about whatever they thought and everyone else would ignore them, because they were clearly an idiot. Then came the internet, and these idiots started to find each other. They formed a group of idiots, sharing their idiotic ideas. Everyone else ignored this group because it was clearly filled with idiots.

Then the villagers who weren’t quite that stupid started to see this group of people talking. The group was large enough that they didn’t notice their village idiot in the group. Of course there’s a bunch of them in there, so they must know what they’re talking about, right? So the next level of stupid up the chain joins, and this continues on up until you have a large enough group following these idiotic ideas with no basis in reality, and a faux belief in being right solely because they’re in a large group and no one knows that it was started by the obvious idiots.

These groups merge and meld ideas, occasionally grabbing onto conspiracies that have legitimate roots, usually not. Sometimes they’re right just by sheer chance.