If your morality is just about social cohesion then you can justify actions that only hurt those outside your social group, such as imperialism and slavery.
Also, the OP was semi-joking (but I do find the idea interesting)
Also, the OP was semi-joking (but I do find the idea interesting)
My point was that a society stratified between free people and slaves, or that invades other countries for resources, can be internally peaceful. Does that make it just?