It is sometimes argued that ideal theories in political philosophy are a form of ideology. This article examines arguments building on the work of Charles Mills and Raymond Geuss for the claim that ideal theories are cognitively distorting belief systems that have the effect of stabilizing unjust social arrangements. I argue that Mills and Geuss neither succeed in establishing that the content of ideal theories is necessarily cognitively defective in the way characteristic for ideologies, nor can they make plausible which mechanisms ensure the alleged negative effects of the widespread acceptance of ideal theorizing. This does not mean that all hope is lost for the ideology objection, however. By turning to a second Marxian model of ideology, I argue that the ideological character of ideal theories is not so much a matter of their content, but rather of their form. Ideal theories falsely present the normative concepts that they use as semantically practice-independent and thereby block potential challenges from subordinate groups to dominant ideologies. It is therefore not the normative content of ideal theories which proves to be objectionable, but the particular role their concepts play in wider political discourse.