We are still learning.
Humans do not automatically know to do the right thing in the right circumstances, nor do we operate as a hive mind to prevent individuals from choosing to do the wrong thing. In order to get a good picture, you need to take humanity as a whole, rather then focusing on the worst of us, and on a scale of centuries, rather then focusing on specific events.
Here's what we do know. When you broaden the scope enough, you find that we are actually living in the most peaceful period in human history. The reason it doesn't seem like that is because the availability of information has increased millions of times greater then what it has been in the past. It used to be a partial genocide was just how wars were fought, and when a victorious leader decided to not brutally massacre their enemies, it was an unheard of act of mercy. Nowadays genocide is rare, and most conflicts are begun and ended without one taking place. That's not to say it doesn't happen, but the frequency of genocides has dropped significantly over the past century in another few hundred years they will be completely unheard of.
As for the whole animal cruelty thing, I don't think it's fair to judge humanity as a whole by the actions of a few. We as a society reject deliberate animal cruelty, so why should we be condemned because a person uses their own free will to make the wrong choice. Because if you condem humanity for this, you are actually condemning free will.