Why should it be an eye for an eye?

Check out the full quote from Matthew 5. Jesus brought a new understanding to the table. Turn the other cheek doesn't mean show no resistance to your hater. Turning the cheek forces the hater to hit you with his palm (like a man and not like a dog). It is a paradigm shift in the way peace can be used in conflict resolution. The main point is to reclaim an equality weather that means you must suffer or not. The first mile you are a slave, the second mile you are an equal.