There are 2 kinds of people in this world, the warlike and the pacifistic
Hutus and Tutsis, farmer and the cowman, Iraqis and insurgents, on and on. We will always have people who want to fight and make war and on the other hand people who despise killing. The only way the pacifists can stop the warlike people is to kill them, which would entirely defeat their purpose, now wouldn't it. Even if they did manage to kill us all, had they the stomach for it, our type would keep popping up in the general population. Unlesss they find the warlike gene and eradicate people who carry it. Of course an entire world populated by a bunch of self righteous liberals would be pretty rough. How would they keep their feelings of moral superiority if everyone had the same opinions as the next person.