http://www.southparkzone.com/episode.php?vid=1009
One of the best episodes ever, minus the Hardily boys, full episode if you never saw it.
Kyle: Will you shut up about 9/11!
Cartman: Kyle, why are you so afraid of the truth?!
Kyle: Because anybody who thinks 9/11 was a conspiracy is a retard!
Cartman: Oh really? Well did you know that over one-fourth of people in America think that 9/11 was a conspiracy? Are you saying that one-fourth of Americans are retards?
Kyle: Yes. I'm saying one-fourth of Americans are retards.
Stan: Yeah, at least one-fourth.
Kyle: Let's take a test sample: There's four of us, you're a retard, that's one-fourth.
Cartman: ...There are soo many people who know the truth, Kyle. Uh Butters! [sees Butters walking towards the group]
Butters: Hey, fellas!
Cartman: Butters, do you think 9/11 was just a plot by some angry terrorists, or do you think there was some kind of coverup?
Butters: Well, I heard that 9/11 was caused by President Bush.
Cartman: Aha! Do you see?
Kyle: Where did you hear that??
Butters: [points] From Eric.
Cartman: I rest my case.
Kyle: [walks up and stands next to Butters] Butters, you don't really believe that, do you?
Butters: Well, l-uh, I mean, uu, you never know. Uh the government does some pretty spooky things. The government and the corporations headed by the Jews that tear down 9/11.
Cartman: That's right, Butters.
Kyle: Goddamnit, you see what happens when you spread this stupid crap, fatass?!
Cartman: What?! People see the truth?!
Butters: Can I go now?
Cartman: You guys are blind!! I can't believe that everyone here is just buying into what they're told by the media! [begins to move away from the boys] I'm gonna go find out the truth. I'm gonna blow the lid off this whooole 9/11 conspiracy once and for all! [goes around a corner and disappears]
.....
Bush: Boys, you don't understand. People need to think we are all-powerful. That we control the world. If they know we weren't in charge of 9/11 then... we appear to control nothing.
Kyle: Well why don't you just tell people the truth?!
Bush: We do that too. And most people believe the truth. But one fourth of the population is retarded. If they wanna believe we control everything with intricate plans, why not let them?
........
Kyle: So then, who was responsible for 9/11?
Stan: Whattaya mean? A bunch of pissed-off Muslims.
Frank: [giggles] Yeah. What are you, retarded? [The President and his staff laugh heartily]