Those of us who have had to deal with Biblical criticism are no strangers to academic fields defined by predetermined, highly politicised conclusions which the fields are then constructed specifically in order to "prove", to the exclusion of anything and anyone who might, by adopting a method which does not presuppose the approved conclusion, arrive at a different conclusion entirely.
At least more broadly, Marxists are the past masters of this. But they are very far from unique. "Free" market economics is another example. So is the thinking underlying the racist, misogynistic and class-oppressive population control movement. And so is that currently associated with the theory of anthropogenic global warming (although that is only the latest problem to which the same old solution is proposed), with its attack on proper jobs, on access to a full diet, on mass opportunities for travel, on the right of the poor or the non-white to procreate, and on economic development in the poorer parts of the world.
Of course, all of these are closely connected. And they are all as closed and as fundamentally fake as Marxist historiography or Biblical criticism, which are also, when put into practice, vicious enemies of the poor, the non-white and the female.