How much of what makes humans unique stems from the contingent fact that biologically each of us is capable of killing every other one of us.
How would it have shaken out if we we were divided into castes, some of which were invulnerable?
Or what if we were all invulnerable to each other’s attacks, like tortoises?
My guess is there would be no hate but no love either.
Eric Linus Kaplan 
This is a fascinating idea.