Human beings are born with a tendency towards hurting other creatures for their own good and even pleasure. Leave human kids unsupervised and no doubt you will have a Lord of the Flies situation. It is adults who must teach children that it is bad to hurt other human beings. But in doing so the parent also makes the child weak and vulnerable to the attacks of others who do not have this sense of morality ingrained so deeply. All big questions in life somehow end up being paradoxes.