Dualism is the tendency of the categorizing mind to separate opposites, identifying with one, while rejecting the other; unknowingly refuting the irrefutable truth of the fundamental law of the Universe, illustrated in this diagram.
It becomes pathological when it is the predominant way of handling polar opposites, leading to political polarization, conflict, and suffering, not harmony and World Peace.
1755/94, ‘a way of thinking which explains phenomena by the assumption of two independent and absolute elements’, from French dualisme, from Latin duālis ‘that contains two’, from duo ‘two’, from Greek duo ‘two, both’, from PIE base *dwo- ‘two’.