frandroid

I'm not sure I understand the question. I'm not familiar of any argument of Marx's that claims that the Church ensured "the good functioning of the economic system". Do recall, that as a mode of legitimation, the Church operated in the feudal mode of production. Marx has no love for feudalism, and you shouldn't either. See his "Contribution to a Critique of Hegel's Philosophy of Right" (1843) and the first manuscript in the Economic and Philosophic Manuscripts (1844).