Scale those thoughts to the human populations at the time. To give an extreme example, if Genghis Khan caused the same scale of death today, that would be 800,000,000 dead.
The world today is far better than it was, but nobody said it is was anywhere near perfect.
Of course, there are not more people in slavery today than at any other time in the past, nor does genocide go on especially not in industrial scales.
Scale those thoughts to the human populations at the time. To give an extreme example, if Genghis Khan caused the same scale of death today, that would be 800,000,000 dead.
The world today is far better than it was, but nobody said it is was anywhere near perfect.