L Ron Fuller famously used this kind of case as an examination of different Judicial modes. It can be found here: http://www.nullapoena.de/stud/explorers.html
I think most defences are usually something cobbled together from "self-defence" "coercion" and "being outside of the jurisdiction of the law due to the extreme nature of the circumstances involved". They seem awkward approximations for the gut reaction that the men have done something that can neither be excused, justified or condemned.
I was recently reading up on public international law and came across the principle of neccessity (article 25 in the Draft Articles on the Responsibility of States for Internationally Wrongful Acts). I found this very interesting because it was distinct from a defence of the grounds of self defence and force majeure (unavoidable force) and is formed around the idea that if a state has no reasonable alternative and if the interest is vital enough, a State may not be held accountable for what it is forced to do. I think this makes a better analogy for the gut reaction to the case we're presented with that any talk of self-defence against circumstance (made by one of the judges in the case of the speluncean explorers). If it were to be applied by analogy to this case, it would clearly clash with the case law Nate referred to earlier as it doesn't consider transcendental values that might be attached to the value of the human life, or deontological axioms that traditionally frame killing as inexcusable.
I find the whole thing rather fascinating, but more as a study of what the law can and cannot do than as one of the nature of man.


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