I also think that simple exposure to a narrative, whether it has any actual facts/data backing it up or not, is likely the primary driver of people believing it.

Now, consider that in most "free speech" societies, those with money can repeat things many orders of magnitude more than others. Over time, this results in influence. Thus, while many countries have "free speech," I'd say they don't have "fair speech." The two concepts complement each other, but one is not the opposite of the other.