Quote Originally Posted by Reddish Mage View Post
Should we imagine inhuman creatures existing possessing very alien and evil intelligence that must be dealt with categorically, the differences between human beings become so superficial that it is immediately obvious how petty those difference are when there is a point of view for comparison.
While intelligence is hard to define, almost all definitions include the ability to learn. Any intelligent creature can learn, and therefore can learn to respect human life.

Of course, physiology or pre-existing culture can make teaching a non-human intelligence to respect human life impractically difficult. So if you want a story where humans are in the midst of an effectively unresolvable conflict with an species of non-human intelligences, such a story is certainly reasonable. But suggesting that an intelligence is unalterably evil, rather than that we lack the ability to alter it, fails to recognize a key element of intelligence.