Filial duty

Suppose a terrorist outfit kidnaps a father and son. Say the father is 70 and the son is 25. They separate them. They make the father an offer: they will kill one and let the other go. He can choose.

I suspect most cultures think a good father would lay down his own life to save his son. 

Suppose they make the son the same offer. Now, there's a sense in which the son has far more to lose than the father. His dad could die of natural causes at anytime, whereas the son may well have another 50 years or so ahead of him. 

Yet I suspect most cultures would consider it profoundly dishonorable if the son sacrificed his father to save himself. An act of supreme disloyalty. 

So there's more to ethics than a cost/benefit ratio, although that's sometimes germane.