The remaining team members have to work and live together after they eat Whetmore, and not letting Whetmore withdraw even when his life is at stake sets a precedent that will tend to cause the members to allocate more personal resources towards the zero-sum game of getting and holding power and decision-making ability in the team.
Note that electing a leader and giving him the power to make life-or-death decisions does not suffer from the same problem. (That, by the way, is an illustration of Mecius Moldbug's general observation that formal power is often superior in its effects to informal sources of power like vague personal obligations and the power to persuade.)
Of course there might be other processes that work even better than electing a leader, but having a leader seems to work well for life-or-death decisions and for situations in which there is no time for debate.
I see it as a case of "emergency micro-government", and not taking part of the voting doesn't mean you're exempt from the laws - that would be like not paying your taxes because you voted for the party that wants to lower them, which lost the election.
i.e. the group should have one way of taking decisions that can apply to the whole group.
However that doesn't mean the decision can't be morally wrong - if the decision to sacrifice one did indeed increase everybody's expected chances of survival, then it was right, but maybe Whetmore's change of mind was right - maybe waiting one week did have a high enough chance of saving everybody. I think that aspect weights more than Whetmore's change of mind.
It depends, I think, on how you view "agreements" of that sort.
One view is that such an agreement is a contract, and in this case the contract apparently did not contain a clause covering opting out. Absent such a clause, unilateral withdrawal does give the others ground for their "breach of faith" argument.
A different view is that what was agreed on was a plan, not a contract. That's a substantially different frame: a plan is a collective course of action in the pursuit of a goal. "Breach of faith" has no place in goal-seeking behaviour; someone objecting to the plan either has a sound case or doesn't.
Breach of faith or not, Whetmore's actions strike me as not entirely well-thought-out. He would have been in a better position had he declared: "Wait, we haven't covered all bases yet; how should we handle the case when one of us is tempted to opt out?" Presenting the case as hypothetical and preserving the symmetry of the situation would have been tactically much better, under both the plan and the contract views. Under the plan view he could have ensured a dispassionate hearing for his proposed alternate course of action; under the contract view he could have pushed for fixing an oversight in the original formulation.
(N.B. I haven't RTFA, just the summary.)
There's an implicit benefit of the arrangement, which is the group not descending into anarchic conflict. Whetmore can't help but benefit from this unless he leaves the group entirely.
I think it'd be interesting to know how different people model the situation. The most obvious option for me is to view it as a form of micro-governance. Randomised cannibalism of one's peers seems almost ridiculously civilised.
Utilitarianism as most people practice it is not strictly about how many people live or die. Killing someone "fairly" and according to a predetermined set of rules presumably seemed better to the survivors than killing, say, whoever was least able to defend themselves, and worse to the survivors than eating someone who had died of natural causes, even though in all three cases the total number of survivors was the same.
I would certainly prefer the outcome (1 person dies, everyone else feels really bad about it) to the outcome (2 people die, everyone else doesn't feel bad). I think most people would in this experiment, with a small group of survivors. But there exists a number of people involved (I'll say it's smaller than 3^^^3) so that I would prefer outcome A to outcome B.
Therefore, considerations beside death could theoretically be significant, and utilitarianism can't be simplified to body count.
A fictional legal case about a team of explorers who got trapped in a cave and ate one of their own to survive. Summary:
Was it right for them to kill and eat someone who wanted to opt out of the arrangement?