I did a quick google of 'origins term "politically correct"' and came across a linguistics discussion list that also suggests the connection with Maoism -- maybe my guess was right.
Most of the references folks are using here are from the 1980s, when PC was already mostly pejorative and ironic. What's odd is that for a short while in the late 1960s and early 1970s, in the US, the term was used unironically in the Maoist sense.
The ironic, even oxymoronic, use of the term is based on the idea that all politics is opinion; there can be no such thing as a "politically correct" idea. The term is as impossible as correct or incorrect art.
But the Maoists believed that through scientific political analysis, the party could discern the one true, or "correct" political line:
Here is the website and some excerpts, which I admit are selective:
http://www.linguistlist.org/issues/5/5-1230.html>
> Based on dim personal recollections, my sense of the latter term
> is that "politically correct" first surfaced in English in Maoist
> literature. There it was used with a straight face, since
> correctness was viewed as being, like everything else, subject to
> constant definition and redefinition by the Party. I recall
> feeling that this world-view implicit in the phrase was so
> contradictory to democratic ideals that only a person who accepted
> political authority over truth could possibly use it without
> ironic intent.
>
> Does anyone have any more concrete data on the history of this
> politically loaded expression?
>
<snip>
The term seems to have entered common use in anglophone Canada first of
all as social democrat teasing of the Maoists and the Stalinists
for their pomposity. "Correct analysis" could be used in the same way, as
in, "You have the correct analysis, comrade," for "I agree with you."
this could be said only to other socialists, of course; the totalitarian
left never got the joke. "Politically correct" was - and in safe company
still is - used by the democratic left in self-mockery, as in: "We have
politically correct fruit salad tonight, _no_ California grapes." The term
seems to have become pejorative as it has been taken over by people who
are incapable of seeing the comic side of their own ideals.
================================
But notice that TODAY the American Right uses the term as a PEJORATIVE
term for virtually any notion with any kind of ethical motivation. In so
doing, the Right derides not Maoism, but the ideology of classical liberal
democracy society, where redefinition does not occur by the party running
a one-party state, but by free and open exchange of ideas, and where
ethical concerns (as well as pragmatic concerns) are relevant.
<snip>
A few years ago when reading Krushchev's secret speech in which he denounced
Stalin for the first time (at the 1956 Communist Party Congress) , I noticed
the use of a term in Russian that could be translated as "politically
correct." While denouncing Stalin, Krushchev maintained a belief in the
"politically correct"--which Stalin obviously wasn't.
================================
Re: Mark Mandel's inquiry about the origins of "politically correct":
Ric Dolphin's Not Politically Correct (1992) confirms Mark's belief that the
term originated in the Thoughts of Mao Tse Tung. Dolphin states that its
first use in the U.S. was by Angela Davis in 1971 when she argued that there
could be no "opposing argument to an issue which has only one correct side."
Then in 1975, the then-president of the National Organization of Women said
that organization was moving in "the intellectually and politically correct
direction." The 1971 quotation seems to confirm Mark's view that only those
who accept political authority over the quest for truth could use the term
with no ironic intent.