Animals don't kill each other for fun, they kill each other for food.
Humans kill each other for fun and for materialistic gain, for the destruction of our home. Having an elite group of sociopaths is a man made system.
Society can't even get along with Laws, it would be worse without them.
We would still have the law of nature, the law of attraction, karma, what ever you would like to call it. Do you really need the government to tell you not to kill people or can you fathom that piece of moral code by yourself?
Yes - you do really need the law and the police to stop people being killed and robbed. Couple of years ago in London there was a riot and the Police let it be known that they would only be protecting life - not property. Within 6 hours, people were being burnt out of their homes, there was widespread looting and people were beaten to death in the streets within 48 hours.
That's the law of nature. Our legal systems are a collective effort to have something better.