Why does America still have Capital Punishment in some states??

Jesus Christ was teaching to ordinary people, not heads of state. It is the business of the state to enforce criminal penalties, but it is not the business of an ordinary person. Jesus did not say that there should be no criminal penalties, just that we should commit no retribution against one another. If someone should strike you, you should not resist, but does that mean they should not suffer the consequences? Suppose a man kills your son. You should not kill him, but the state has a responsibility to protect every citizen from this murderer, not for retribution, but for the well-being of society.