Fear is a major factor in many of the conflicts in the novel, but I don’t think it’s the sole cause of conflict. Fear predominates the first part of the story, when Genly is in Karhide. Genly’s mission is to bring the people of the planet Gethen to join the Ekumen, a loose federation of human worlds. To do this he must convince Gethen’s two distinct societies to agree to the union. The first one he approaches, Karhide, does seem to refuse the prospect out of fear. They distrust the unknown and are resistant to change. While in Karhide, Genly also shows fear himself in his relationship with Estraven. Estraven is genderless and formal, and he communicates in a style that is utterly unfamiliar to Genly; this causes distrust and suspicion.
But when he goes to Orgoreyn, one could argue that it is Genly’s lack of fear that gets him in trouble. The people in Orgoreyn communicate in ways that feel more familiar to Genly than the ways of Karhide. This familiarity makes him feel safe, despite Estraven’s warnings, and Genly is less cautious than he should be. His lack of fear leads to his arrest and subsequent condemnation to a work camp where he probably would have died if Estraven hadn’t rescued him.
I would say that the main source of conflict in The Left Hand of Darkness is assumptions. Genly often gets into trouble by relying on what he already knows instead of being open to not knowing. As he says himself, “Don’t you see how useless it is to know the answer to the wrong question?”