In Orson Scott Card’s Ender Series the concept of Xenocide is introduced. Xenocide is when one intelligent species drives another intelligent species to extinction. A direct translation is stranger killing. In this case xeno- is taking stranger to mean alien, and furthermore, alien not of this world.
Xenocide, in my mind is the most barbaric, evil, and despicable act that can ever be done. Consider for a moment all that would be lost if humanity was to be completely eradicated from existence. The works of Shakespeare, Einstein, Beethoven, and many others would be lost. Now consider what wonders would be lost if humanity were to commit Xenocide.
Let me go back to the word xeno-. As I said it means alien. Consider for a moment that alien simply means someone not of the country that you live in. Consider the tactics that were used by the first Europeans to come to the New World. I would argue that they very nearly committed Xenocide on the populations living here at the time. That is a tragic thought.
My final point is very simple. Humanity must never commit Xenocide. Why? Because if we are an intelligent species (and I do believe that we are) then to commit such an atrocity would serve as an argument agains our claim of intelligence.
If you want to consider this further, please read Card’s Ender series. They are exceptionally well written, and I believe that everyone should read them.

02/07/2011 at 08:12
Well, the word “xenocide” is (obviously) an alteration of “genocide,” the word created to describe the Nazi actions, though it has been applied retroactively, and I’d argue very accurately, to Manifest Destiny and the American Westward expansion.
The British use of smallpox-laden blankets is probably the most vile example I can think of, but hardly the only one.
Anyway … yes, I think it’s interesting that in the books the first act of Xenocide was accidental (to Ender, anyway) and hailed at first, though later he came to be seen as the most evil person ever. By “Speaker for the Dead” Ender’s name was reviled everywhere. Of course, then in “Xenocide” the government is turning around to do it again, only this time with two sentient species simultaneously.