Sentence:  It <WSD>is</WSD> not unfair to add on the other side that the crude and almost vitriolic approach of certain fundamentalist sects toward the cultures and religions among which they work has contributed measurably to this heightening of anti-Christian sentiment . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)