The US today isn't in much of a different boat. Granted, a human being a mushroom is quite an extreme one, but I'm sure a well-crafted documentary reaching a wide enough audience could still have a deplorable impact. Here's a 2013 poll on conspiracy theories:

http://www.publicpolicypolling.com/main/2013/04/conspiracy-t...

I was in high school when one of the "moon landings were a hoax" documentaries made the rounds. A significant portion of my class was instantly converted by the documentary. I lost a little of my faith in humanity at that time, though much of it was quickly recovered thanks to an excellent math teacher who paid attention to his students, found out about the phenomenon, and dedicated half of a class to thoroughly debunking it.