The conclusion of the passage is: "Their motive in advancing this theory must be something other than disinterested concern for scientific truth." The passage introduces a theory put forth by economic theorists about motives of manufacturers. Then a claim is put forth that weakens the first theory, and "anyone who watches television knows" this claim. The passage tells us that economic theorists also watch television. Thus, they must also know this claim that weakens their first theory. So, we conclude from all this information that economic theorists must then have some other motive than disinterested concern for scientific truth. Therefore, the claim that manufacturers manipulate and create consumer demand is merely one of the claims on which the conclusion is based, not the conclusion itself. A good trick to find the conclusion of each passage is to see which sentence all the other sentences are leading up to. Hope that helps!
