It's happened throughout human history. Whole peoples wiped out, or culled down to such a degree that they became obsolete and irrelevant to the land they had lived upon for thousands of generations. Today we are constantly bombarded with the 'thought-bite' that some 6 million Jews perished under the Nazis, yet most of us are oblivious to the fact that 100 million men, women and children perished for the 'good' of Communism in the 20th century. It is amazing how little we today even acknowledge the vast human destruction of the past. They certainly have.
Genocide is history.
Humanity has progressed beyond such things. We believe that human beings are not, as a whole, mass murderers, torturers and exterminators. We believe that most human beings are remarkably decent, tolerant and benign. To actually be 'human' proves this. For the adjective is the same word as the noun.