Like genius and creativity before it, the word genocide has become so horribly misused and over-used that bringing it into a discussion now runs the risk of driving out more people than it might draw in. This is not to say that such things do not happen, only that we have badly damaged our capacity for understanding them, for talking about them, and maybe also for doing something about them in a lasting way.
The word genocide was coined by a man whom history has almost forgotten, and this article about that man — Raphael Lemkin — contains a graf which says more about the problem of genocide than most any other platitudinous hand-wringing I've read:
... [W]e need to force ourselves to think beyond the platitude that genocide is an abomination, and to understand the more difficult thought that it represents an unending moral temptation for mankind. [Emph. mine.] The danger of genocide lies in its promise to create a world without enemies. Think of genocide as a crime in service of a utopia, a world without discord, enmity, suspicion, free of the enemy without or the enemy within. Once we understand that this utopia is the core of the genocidal intention, we have to realize that this utopia menaces us forever. Once we understand genocide as utopian, we understand also the vulnerability of universalism. The idea that there can be a "crime against humanity" is a counterintuitive one that has to make its way against the more alarming thought that what humans actually desire is not a world of brotherhood, but a world without enemies.
There are two ways to live in such a world. The long, complex, difficult but ultimately more fruitful way (albeit fruitful in ways that are often invisible to the immediate observer) is through diplomacy and mutual rapprochement. If two neighboring countries are at war, it is not required that they love each other unconditionally for the conflict to end. They need never love each other. They only need to quit trying to blow each other to pieces. In doing so they may suddenly find they have the energy to do a great many other things that previously seemed out of reach, or just not very interesting.
The other, easy way is just to kill everyone who doesn't agree with you. Superficially easy, as everyone who has practiced it has found out. You have to ignore the possibility of reprisal, of sanctions, of outside intervention, of the sheer logistical problems of dead bodies everywhere, of isolation even from your alleged allies (as such allegiances often turn into contests of ideological purity), of your name becoming anathema across generations. Barrows Dunham once again: the gains hardly seem worth all that degeneracy.
The problem, of course, is that people are by and large not trained — not even in the most advanced civilizations in the world — to see such effects. That, they leave to their grandchildren. Or their neighbors. If any of either remain, that is.