Those who try to include all life when trying to determine justice: Should a man be executed for killing a fly? No? The fly has a short life span? The fly is small? All these rationalizations can be applied to you, by a creature that lives longer, is bigger, etc. #philosophy 

The social contract between all people around the world only has one requirement: Don't kill. From there it's those who don't agree, those that agree but have some reactive justification, and those that agree and don't kill.