It's pretty easy to see how people can believe it. How many have killed themselves to reach a new plain? Or paid for a spaceship to heaven... Or for that matter, how many people are sitting at their computer with a tinfoil hat on right now? At least scientologist aren't a suicide cult. Well, not that we know of anyway. I can also understand how hollywood actors (and such) would fall for it. They're not the most stable of people. Nor the smartest (come on, carbon monoxide killing the planet? it's just hot water. literally!).
But all of that aside, they're freaking out there... it'd take some seriously bad mental conditions for people to really believe it, if they knew all of it.