I agree that there are certain moral rules we should never break. Human beings are not omniscient, so all of our principles have to be principles-in-a-context. In that sense every principle is vulnerable to a black swan, but there are levels of vulnerability. The levels correspond to how wide ranging the abstraction. The more abstract the less vulnerable.

Injunctions about truth are based on the metaphysical fact of identity, which is implied in *every single object* we encounter in our entire lives. So epistemological injunctions are the most invulnerable. The one about not helping the ferry boat captain - well helping him would be an absolute *in normal life*, but war is not normal life. It's a big, ugly, black swan. They should not feel guilty over that poor fellow, because "it's just war." (and I mean that in a deep epistemological sense, not a redneck sense)