As Naremore rightly notes, noir has become a commodity as much as an aesthetic category (seemingly this is the fate of all aesthetic categories; we tire of being reminded of this, however, and routinely look past it whenever possible).
Many critics like to "create buckets" regardless of whether the effort tells us anything worth knowing. This tendency is rampant in noir criticism, and it's part of an exclusionary mindset that actually diminishes understanding. If one is going to do that, one should do it based on a combined approach to the elements-forces-structures that operate within a film, and within the overall creative environment surrounding the creation of such an artwork. Often that involves holding (as Fitzegerald wrote) two contradictory thoughts in one's mind at the same time, which is why it's often difficult to determine if someone with a "first-rate mind" is not also (at the same time) a lunatic... :-)
Ahearn is certainly right that the studios tried to meta-subvert noir's subversive message, particularly in the highly-pitched period from 47-51. But even there, this is just a more extreme manifestation of what goes on with art in general, vis-a-vis those in power. I'm not sure we can claim a true difference of kind there, as distinguished from a difference of degree. Noir elements were awash in the late 40s everywhere, across nations and genres alike, and it is this that we should be trying out best to trace. I often think Ahearn is talking out of both sides of his mouth at the same time, which tends to lead one in circles.