Steven Pinker's excellent piece today in the New York Times "The Moral Instinct" explores these scenarios and suggests that most people would have a problem with that final scenario. Even though you could save people by sacrificing one person, most people have a problem with being responsible for harming one. But it is tough for people to express why this is so.
It turns out that people have an innate moral sense, according to Pinker's article:
When anthropologists like Richard Shweder and Alan Fiske survey moral concerns across the globe, they find that a few themes keep popping up from amid the diversity. People everywhere, at least in some circumstances and with certain other folks in mind, think it’s bad to harm others and good to help them. They have a sense of fairness: that one should reciprocate favors, reward benefactors and punish cheaters. They value loyalty to a group, sharing and solidarity among its members and conformity to its norms. They believe that it is right to defer to legitimate authorities and to respect people with high status. And they exalt purity, cleanliness and sanctity while loathing defilement, contamination and carnality.
According to psychologist Jonathan Haidt, a universal sense of morality can be broken down into five primary moral "colors:"
The exact number of themes depends on whether you’re a lumper or a splitter, but Haidt counts five — harm, fairness, community (or group loyalty), authority and purity — and suggests that they are the primary colors of our moral sense. Not only do they keep reappearing in cross-cultural surveys, but each one tugs on the moral intuitions of people in our own culture.Photo by slack12.