There are plenty of philosophers that rejected the idea that objective consensus is possible, even more so when faced with assigning a truth value to arbitrary phrases. Off the top of my head, both Hume and Kant noted the impossibility of true posteriori certainty. You're quite correct that this is well-tread territory, but you're wrong to think that there's some widely agreed-upon, well-defined theory of truth or knowledge.
Pragmatically, we're completely immersed in floating signifiers and appear to rely on them for fundamental communication, so I'm more arguing for a move to discussion of degrees of certainty & consensus rather than a binary understanding of knowledge.
(...and this is even before diving into gettier problems!)