Agreed. It's arbitrary and situationally changeable which is why societies create laws to nail down the rules.
Consider lifeboat ethics; all the options are valid choices, none are correct. https://en.wikipedia.org/wiki/Lifeboat_ethics#Lifeboat_articles
My two cents: you put the children on the life boat and let everyone else take a swim.
A lot of people thought Plato was wrong, but he thought there was an ideal form of justice and virtue which few people would ever perceive because we live in a world of opinion and illusion.