An argument that cannot distinguish between science and witchcraft is a victory of rhetoric over sense. The distinction between natural thinking and science is at the core of rationality (cf. Hegel, who usefully insists that it is not that they are made of different stuff, but that the latter is a refined form of the former). To say that medical science is just as good as witchcraft is a kind of performance, but nobody who says it really believes it.
That surely is the failure of the sociology of knowledge writ large, its inability to defend the superiority of scientific understanding from superstition. Without that there can be no Marxism, no Darwinism, no critique of religion.