Indeed this is precisely the unwarranted nihilism I'm criticizing, where if we were to believe that consensus in philosophy is impossible, so would philosophica

Indeed this is precisely the unwarranted nihilism I'm criticizing, where if we were to believe that consensus in philosophy is impossible, so would philosophical progress--and therefore knowledge. This is a libelous claim that all philosophers are engaging in intellectual masturbation explicitly aware that their exercises are to be of no progress. The Pyrrhonists, Diogenes, Descartes and others famously believed in this; but Kant fixes this, making the discipline of philosophy possible by proving the scope of reason.