So what if anti-philosophy is also philosophy?

Whenever somebody makes critical remarks about philosophy, the defender of philosophy screams 'but that is also philosophy!' as if criticism of philosophy is somehow necessarily incoherent. Here is Peter van Inwagen's expression of the idea:

"The fate of logical positivism is the fate of all attempts to diagnose the failure of philosophy to produce a body of established fact or even a body of provisionally accepted theory. Such diagnoses are invariably "just more philosophy" and exhibit the very symptoms they are supposed to explain: they are proposed, people argue about them, a few converts are made but only a few, and, in the end, they retire to occupy a Place in the history of philosophy." (Metaphysics, 2014)

Well, so what? Jason Brennan puts it well:

"'Philosophy is irrational' is a philosophical position. If philosophy is irrational, so is the view that philosophy is irrational. If philosophical argumentation never establishes any position, then the anti-philosophy position cannot be justified by philosophical argumentation. The Argument against Philosophy refutes the Argument against Philosophy. Even if this defence works, it is embarrassing if this is the best defence philosophy has. Yet, it is not obvious that the defence succeeds. It may just be that all philosophy is unreliable except anti-philosophy philosophy." (Scepticism about Philosophy, 2010)