that question might be better formulated if, as nathan has implied, 'who' and 'it' is given some more serious prefatory attention.
someone mentioned 'history' and its ostensible defense, against the denial of such by 'pomos', in MR. what tends to be missing from these kinds of arguments is that a very particular understanding of historiography and history is being used as a placeholder for all permissible practices and uses of history as such, and thereby any perceived or actual critique of the former gets read as a denial of history tout court. is MR's version of historiography the only one available? this is, or should be, the debate. but this gets neatly sidestepped by the pretense that this historiography is the only historiography.
for much the same reasons, these debates are almost always an underhanded way of presenting 'marxism' and 'postmodernism', not only as opposed, but as themselves homogenous political and philosophical practices. in many ways, debate on this list has more to do with drawing lines around a permissible marxism than it has to do with debating postmodernism (as either historical moment or philsophical, architectural, whatever project).
that's why it's marxists who are routinely called upon (stalked?) to announce that they have renounced 'pomo' or exposed' as being 'pomo' or simply accused of being such when someone wants to present themselves as more-marxist-than-thou without actually having to engage anything amounting to a marxist analysis.
in short, where nothing substantive is being argued about, but labels and boundaries are being drawn up, mostly with regard to the terrain of marxism itself. as someone else has said, 'show us your identity papers'.
Angela