Even Ayn Rand didn't think that Objectivism was applicable to all situations; she said somewhere that lifeboat situations didn't count, and I think this applies

Even Ayn Rand didn't think that Objectivism was applicable to all situations; she said somewhere that lifeboat situations didn't count, and I think this applies more generally to all extreme situations: neither reason nor evolutionary psychology is guaranteed to help you decipher the ethics of actions in situations which are extremely unlikely to occur.