I think sometimes we forget that although we are the dominant species on this planet we are still just a species that has evolved from the same roots as all the rest. Compared to other species that are (and have been) on this planet, we haven't even been around very long. Relatively speaking, we are a fairly young species and it wasn't very long ago that we would have thought that clubbing each other on the head for a scrap of food or a better mate would have been quite justified. I'm fairly certain our earlier ancestors would have had a "take what you want" attitude whether it be food, territory or a mate and speaking from an evolutionary stand point that attitude would have been in part what made us stronger. Luckily as we progressed we found it more beneficial not to kill within our families, tribes, clans and territories and eventually "love thy neighbour" and "thou shalt not kill" became religious teachings - provided thy neighbour didn't form it's own religion or oppose your government or (depending on which part of which country you live in) threaten you with bodily harm or try to steal any of your shit. Then it remained justified.
Now most species have been quite content to spend their lives finding and protecting a territory, finding food and finding a mate but the human species has not been quite so complacent. We've created art and architecture, learned to fly, mapped the planet, the stars and the human genome. We've looked deep into the universe and deep into the nucleus of a single atom but for all our achievements we are still that same species that took what we wanted, when we wanted it. Those instincts still exist. Although most of us agree that certain behaviours are wrong and have the ability to curb them, there are still times when our ancient barbaric instincts surface. If our species survives another hundred years or hundred thousand years, this may still be the case. Like it or not we may be stuck with them. Humans innately want power. The power to take what we want and who we want and this instinct has surfaced in all forms of art whether it's sculpted, painted, filmed or written.
Still, I think the fact that we've gone from wandering naked on the plains of Africa with nothing but a shard of rock for a tool to watching the Mars landing on our home computers in the last hundred thousand years or so says a lot for our species. The crocodile has been around for millions of years and when's the last time you saw one of them build a spaceship?