Click here to access article by Ron Unz from The Unz Review.
Unz not only finds the origins of this widely used smear to suppress real conspiracies, he also touches on a broader subject that is of interest: the post-WWII ideological takeover by fascist forces in the US. Those US major capitalist players (along with capitalists with other Western countries) who helped fund Nazi Germany hid under the more legitimate label of "isolationism". They vigorously opposed getting into the war against Nazi Germany and hoped that the latter country would realize Hitler's well laid out plans contained in Mein Kampf to crush the Soviet Union, the arch-nemesis of any true blooded capitalist. These corporate and financial interests together with their right-followers constituted a fascism-prone wing of the US ruling class. The knowledge that this ruling class faction took control of our nation after WWII is a well-suppressed secret.
The fascists had long infiltrated the State Department and secret services like the FBI, but after WWII they accelerated their development of, and infiltration in, largely unaccountable secret services like the CIA, NSA, and 14 other such services. Numerous non-profit right-wing think tanks soon proliferated to promote their new right-wing ideology. This subversive right-wing faction also developed strong ties with corporate media, Hollywood, and all major ideological institutions to influence their coverage of news, information, and ideology.
Unz essentially describes his awakening from the cult-like ideology of this new faction starting in the 1970s and '80s to realize that a major ideological shift had occurred to suppress political conspiratorial ideas that were previously permitted in the pre-war years.