Wiping out people is never an answer, name me one genocide that has done the human race good.
Though this may be an off-topic now, since we all (myself included) care about our fellow Bay12er's in more dire circumstances than our own, I would like to answer this supposedly hypothetical question. Before I start, however, I'd like to add the disclaimer that I'm not advocating Genocide here. Genocide is inherently destructive, and does not begin to respect the worth of every human life. It is not, and I will repeat, not something that should even be considered, much less put into practice. However, just because the means are inherently evil, does not mean that "good" ends cannot be achieved. I believe that the ends do not justify the means, but there are people who think otherwise...
I present to you two cases. The first involves the destruction of Troy by the Greeks. This genocide of the Trojans (if accounts are to be believed) directly led to the establishment of the Greek colonies in Asia Minor, which itself spread Hellenism and Greek culture, including mathematics, philosophy, and the arts. In addition, though the point could be argued, I feel that the Greek colonies effectively divided the Greeks, enough for Alexander and his father, Phillip, to conquer the Greek homeland without severe losses. This in turn led to the further spread of Hellenism throughout all of west Asia, as well as Egypt. If we consider the spread of Hellanism to be a good thing (which I do, considering the Greeks were among the most advanced civilization of their time) then the Trojan genocide was most certainly a good thing.
The second case, which is a little less ambiguous and less open to argument, would be the oft-mentioned destruction of Carthage at the hand of the Romans. Though again, you might see the spread of Roman influence as a bad thing, it is very clear that the spread of the Roman Empire enhanced the culture and scientific understanding throughout the Mediterranean, and led to an era of peace (Pax Romana) that has never been rivaled since. It is perfectly reasonable to assume that Rome could not have made its great achievements without the complete and utter destruction of Carthage. If nothing else, the Carthaginians had proved to be immensely capable of coming back from defeat and continuing to prosper (after all, they were defeated twice before and still put up a good fight).
Given, both of these examples are ancient, mainly because since ancient times, no-one has had the guts to completely and totally annihilate an enemy (except Hitler, but the Jews weren't really an enemy nation, per se; it would have been more interesting to see how Poland would have turned out). That's why genocide doesn't work, because you have to be thorough. You have to completely grind your enemy into the dust. There will be peace on earth when thermonuclear war wipes us all out.
Again, the disclaimer that I DO NOT support genocide in any form. I support historical awareness.