No evangelistic erroneous network of ideas can guarantee the satisfaction of these two demands : (1) propagate the network without revision and (2) completely insulate itself against losses in credibility and adherents through criticism. If a network of ideas is false, or inconsistent or fails to solve its intended problem, or unfeasible, or is too costly in terms of necessarily forsaken goals, its acceptability may be undermined given only true assumptions and valid arguments. People prefer to adopt ideologies that (i) (...) are logically consistent, (ii) are more truth-like and of higher information content than their rivals, (iii) are systematically organised, (iv) solve their problems better than their rivals, (v) do not contain unfeasible demands, and (vi) do not contain uneconomic demands. Truth and validity therefore act as Darwinian-like filters on ideologies. Using Popper's notion of situational analysis and with reference to Darwinian evolution, considered as a special case of the former, and Bartley's theory of comprehensively critical rationalism I argue that a propagandist cannot guarantee his message or his movement from sound criticism. All positions are in a methodological sense open to argument. Moreover, the logic of a propagandist's situation constrains him into making his message and himself open to criticism in order to maximize its chances of being propagated through the population. But he then loses control of the message in two respects. Firstly, his audience are disposed to select from the competing ideas they encounter those that satisfy (i) to (vi) because of man's evolutionary history. Secondly, he cannot guarantee protection from criticism even a privileged section of his message because he cannot predict in a systematic way what logical repercussions each protective reformulation of the ideology will have on other sections of the ideology and what criticism the ideology will encounter. He cannot do the latter because of certain logical properties of theories that endow them with unfathomable depths. Marxism and Freudianism serve as case studies, especially for the analysis of Popper's notion of the immunizing stratagem, a methodological/logical device that is supposed to save theories from criticism. "Immunizing stratagems" either abandon the ideology they are meant to protect or seriously lower its chances of being reproduced. (shrink)