If left to their own devices, as sooner or later they will have to be, these monsters will remove themselves from the human gene pool. No one can force them to function in a merely humane and reasonable fashion.
We seem to have enough trouble toeing the mark ourselves, what with waterboarding and blowing up wedding parties.
In fact, we role modeled the Nazi "solution" for Hitler and his thugs by our treatment of the indigenous peoples of this land. This is documented in the writings of some of the monsters of that regime, including Reinhart Heydrich...considered one of architects of the holocaust.