Drawing on empirical evidence from history and anthropology, we aim to demonstrate that there is room for genealogical ideology critique within normative political theory. The test case is some libertarians’ use of folk notions of private property rights in defence of the legitimacy of capitalist states. Our genealogy of the notion of private property shows that asking whether a capitalist state can emerge without violations of self-ownership cannot help settling the question of its legitimacy, because the notion of private property presupposed by that question is a product of the entity it is supposed to help legitimise: the state. We anchor our genealogical critique in recent work on ideology in epistemology and philosophy of language, and in current debates on the methodology of political theory. But, unlike more traditional approaches that aim to debunk whole concepts or even belief systems, we propose a more targeted, argument-specific form of ideology critique.