I think the rise of such theories has a lot to do with the fact that the 70s and 80s replaced the 20s as the Golden Age of Cynicism in America -- everybody was lying to everybody else, and making a lot of money doing it, so why *not* believe that NASA in on it too. If you want to see the origin of the modern snark-everything-all-the-time/sincerity-is-for-chumps ethos, you need look only to that period. The twenties had their share of cynical frauds in high places, but they were pikers compared to their grandchildren.
+1
(that's gonna be my excuse from now on!)