[Edit: Due to some confusion, I'll state explicitly that the "dualism" here is a tongue-in-cheek way of describing a real issue.]
It's one of those charges made against Gnostics that gets some folks riled up, Dualism. Is Dualism a bad thing? The people run in horror from the idea are largely heresiologists, but lest we dismiss it, there are some modern Gnostics among them. Personally, if all someone means by a “dualist” is someone who can't see a way to reconcile or erase the distinction between spirit and matter, that is as good a description of the way I understand things as any other.
However, there is a distinction between simply being a dualist in that sense and being a “Radical Dualist.” Radical Dualism includes assumptions about the ultimate nature of the two things, that they are two different metaphysical “substances” or have two distinct origins in some ultimate abstract philosophical sense. As someone much more in line with the Pragmatic school of Philosophy than the Scholastic one, I have a hard time even caring what this entails as an assumption in an abstract game. People at least assume that Radical Dualism implies an exclusive-or for all relevant choices between the two things. An exclusive-or is just short hand for “either this or that, but not both this and that.” In this rather narrow understanding, one could not value spirit, and also value matter, for example. If that isn't scary in and of itself, think of how embarrassing it would be to have radical dualistic ontological assumptions kicked in your face by a Thomist on the beach.
Any limited form of dualism is incomparably better than the Radical Universal Dualism most people practice. That kind is horrifying, if you you are someone who likes to think, read, write, and discuss. And it should be embarrassing, yet there doesn't seem to be any even when people are caught doing it time and time again.
What is Radical Universal Dualism? It is being a Radical Dualist about well, everything. The turning into a universal law the fallacy “you're either for it or against it.” This is black-and-white thinking, wherein the exclusive-or is the only relationship. Any criticism is taken as an outright rejection, taken to mean that you are against the larger whatever in it's entirety. This is the Modern Dualism that has me longing of the old fashioned kind. (Gimme that old time dualism. Gimme that old time dualism. Gimme that old time dualism ...that made hereseologists wee.)
Is it possible to be critical with these Modern Dualists about? This is a good question. Let's look at the nature of this for a moment. If someone makes a specific criticism, how far can someone else legitimately take it?
If someone is critical of a particular brick, can they be taken as being critical of the wall, bricks in general, or of masonry, or of building, or of civilization? I would say that it is unclear whether they are being critical of the wall but you couldn't assume that is the case, the rest is ludicrous. Yet if we look at modern discourse, the rest is the norm. If someone merely stops at the assumption that they want to tear down that one wall, they are being unusually generous.
To take a recent example: how far can one take a criticism of assumptions made by Theology? Can it legitimately be taken as being critical of critical thinking, the analytical method, or of religion? No, it cannot. Can a statement about the impossibility of a theological definition of Gnosticism be taken as a statement against any definition of Gnosticism? No. This part of Modern Dualism is “expanding the scope.” The statement or criticism is widened in scope by others.
When scope-expansion is combined with the exclusive-or we get what seems to be the model for all of this, modern political speech. Perfect for sound bites, and for convincing the already convinced. However, it does not exist to constructively engage in anything. It turns discourse into a rhetorical game. Conversation into a series of misunderstandings. It is a way to get ratings and win elections, nothing more.
How can we avoid this? Try to not expand the scope on someone else's behalf. You can say that a statement implies a larger scope, or take a look at the argument from a larger scope for some reason, that is being aware of, and being clear about, what you are doing. And, don't think every relationship between two things is an exclusive-or, very few truly are, although it is a favorite rhetorical device to pretend otherwise.