Hickey is a good representation of human evil
The character of Cornelius Hickey (an assumed name, as the character murdered the real Cornelius Hickey and assumed his place among the crew -- presumably to escape the justice that was coming for him) is a good metaphorical representation of human evil in general. He's the only out and out villain among the human crew. (And even there, note he's not absolute evil -- when Dr. Stanley insanely burns down the camp, during the carnival, Hickey acts , morally, rationally and correctly to save the crew. This is good storytelling, and recognition of basic reality -- even the worst of people are not such that they have NO good in them at all.)
But Hickey is evil. He's a sociopath. However the real, historical Franklin expedition may have played out, in this dramatized account, he is the chief architect of everyone's demise. The expedition may have been doomed to failure from the start -- failure as defined by achieving its goal of opening the northwest passage -- thanks to imperfect planning, thanks to penny pinching by the British admiralty that led to the purchase of compromised provisions, thanks to the political appointment of a pompous and incompetent commander. But it might have been possible for good leaders to save most of the men, and bring them back home again, but for the malicious work of Hickey. Crozier came up with a workable plan, and he won the loyalty of Fitzjames and the other officers to effect it. But the one, BARELY possible chance of survival -- which hinged on winning the help of the native Inuit peoples, was destroyed once Hickey decided to frame the Inuit for killing an officer, all in order to keep his planned mutiny alive -- a mutiny in which he assumed a leadership role. ONE man, determined to follow his own self-aggrandizing plan, destroyed any hope of survival the rest had.
This is the essence of human tragedy. All it takes is one evil man, selfishly pouring poison out to all who will listen, to undo all the strenuous efforts of dozens of good men.