I have already replied to various objections to pluralism in my article IS ONTOLOGY MAKING US STUPID?, which is published online in THEORIA. I will quote from the pdf version, as it has page numbers, for easier reference, available here.
On the pluralist’s supposed inability to distinguish the validity of scientific claims from those of the Voodoo priest, I write:
“The difference with relativism is that there is no guarantee that the approach will work, Being is independent of us and must respond positively, which is often not the case” (p14).
This is one of the most important differences between pluralism and relativism, the absence of a guarantee to validity, the refusal of the infallibility (“everyone is right in his own reality”) that accompanies naive relativism.
On the problem of dogmatism or lack thereof, I write:
“the determination of what is real and what is a simulacrum cannot be the prerogative of an abstract ontology, and thus of the intellectuals who promulgate it. There is no fixed framework, the manifest realities are multiple, and Being is unknowable. Thus the determination of what is real depends on our choice in favour of one form of life or another, ie on a political decision. This leads to Feyerabend’s conclusion: ontology “without politics is incomplete and arbitrary” ” (p14).
This multiplicity of frameworks is the necessary complement to the fallibilism described above. Our theories are fallible and must be tested against the real, but this real is more malleable than the monist realist presumes. Being does not respond positively to just any idea, and it certainly does not validate the attempt to cure epilepsy by exorcism. However, Being does respond positively to a multiplicity of modes of existence, from that of the Homeric Greeks to the atomic physicist’s form of life.
Yet another important difference between pluralism and cultural relativism, is that pluralism rejects the relativist’s idea of a fixed framework closed off from others (what the structuralist relativism of Niklas Luhmann calls “operational closure”:
But one could object that Feyerabend is a relativist and so that “empirical research” for him could give whatever result we want, because in his system anything goes. In fact the best gloss of this polemical slogan is “anything could work (but mostly doesn’t)”. Feyerabend’s epistemological realism is supported by an ontological realism: “reality (or Being) has no well-defined structure but reacts in different ways to different approaches”. This is one reason why he sometimes refuses the label of “relativist”, because according to him “Relativism presupposes a fixed framework” (13)
Feyerabend’s argument is that we do in fact communicate with members of other traditions, and that traditions themselves change over time as a result of these manifold exchanges.