imagine you’re traveling in a vessel which holds three people. there are blue vessels and red vessels. upon every trip, two occupants will experience organ failure. in the blue vessels, they will simply die. in the red vessels, the third one will be sacrificed and their organs harvested to save the other two.
obviously all travelers will want to take a red vessel, because it cuts their risk of death in half. this by definition means that the laws of the red vssels are more ethical. the more ethical system is by definition the one that a self-interested party would choose if they were unsure of their identity.