Despite Roy's fears of how the discussion will evolve,
I do wonder what Mises was talking about.
  http://mises.org/humanaction/chap3sec2.asp
Was he just getting away with murder by calling "Marxian"
anything vaguely to the "left" that he felt smacked of
polylogism?  Or is there textual evidence that Marx
seriously argued for polylogism?

Just to be clear, I do not consider that an argument
that behavior (including argument) is influenced by
ideology amounts to an argument for polylogism.
Mises does seem to conflate the two
http://mises.org/humanaction/chap3sec3.asp
Perhaps someone can provide context for why he would
feel justified in doing so.

Would it be reasonable to say that Mises underlying
concern was that Marx's analysis of how certain economic
ideas might proliferate and find support *due to* their
contribution to system legitimation could be (and has been)
mistaken for a reason to discard these ideas?  This
really has nothing to do with polylogism, afaics.

Additionally, Mises's apparent claim that we should
be puzzled by the idea that a false belief could serve
us better than a true belief appears truly naive.
   http://mises.org/humanaction/chap3sec3.asp
(It has often been to believe in ideas conflicting with the
dominant ideology in so many places and times, and pretended
belief serves less well than reflexive belief in many
circumstances.)

Finally, as a tiny test Marx vs. Mises in the understanding of
ideology and property, I wonder if it is useful to consider
the recent evolution of intellectual property law --
bought and paid for in the copyright industries and oddly more
resistant in the patent industries, but promoted
always through well-funded and rather successful
efforts to persuade us all that (contrary to the Constitution,
in the US) creators are not granted a social privilege of temporary
monopoly but rather have a natural right to every last penny that might
possibly be squeezed out of a creative idea, from here to eternity.

Thanks,
Alan Isaac