People who say that humans are mostly good have never watched babies play.
You can tell a lot about the human species by observing the newest, most innocent, utterly unsullied additions to the race; sweet little babies.
Have you ever heard the story of Jacob and Esau? It's a warm and fuzzy tale that goes something like this:
Jacob and Esau were twins who hated each other as little fetuses in their mother's belly, and that bitter rivalry lasted the rest of their lives. Jacob even tried to pull Esau by his leg back into the womb while Rebecca was birthing them. That's some shit, right? If you don't believe me, go ahead, look it up. It's right there in Genesis. Little warring babies.
But it's not just Jacob and Esau with the problem. Not only have scientists proven that babies fight in the womb, but they continue these violent rampages into babyhood and beyond.
There seems to be an innate felon within us all. This can be clearly observed by watching babies "play". From day one, it's instinctual to want to take what someone else has. Let's just go ahead and call that what it is: blatant theft. Yet this is our first instinct. If we aren't able to get what others have by conventional means, then we immediately resort to physical violence to obtain it. And babies don't care. Babies don't give a shit. Just watch as these twins duel over a toothbrush.