That situation (sacrificing the least useful members to save the more useful ones) is perhaps Utilitarian or even Machiavellian. One could argue in a rather cold-blooded way that the end result would be for the best, and would justify the means.
We had endless discussions along these lines in Moral Philosophy, usually involving whom one would chuck out of a hot air balloon or a life raft in the Pacific Ocean. It makes me think that, in addition to 'fair' and 'reasonable' there is 'humane' or even 'kind', principles that are much harder to define or to practise. One can't act on mere emotional promptings alone, and it can be dangerous to follow one's 'conscience' or 'heart. I'm sure Hitler himself thought he was doing the best for Germany. And look at those dreadful exorcisms of child witches that take place in, say, Nigeria even today. Presumably the protagonists think it's 'all for the best'

Philosophy is a forest full of briars and unseen traps in the undergrowth! Finding a path through is never easy...