[Preechr]

All cultures have considered murder bad behavior, though many cultures have disagreed on what constitutes murder. Aboriginal tribes, much like your Romans or Old Dixie slave-owners, had a narrow view of what they considered real people, and most of these early societal types considered the murder of whatever they viewed as a real person less than moral. Roman Senators did not approve of the killing of another Senator with no just cause no more than did a slave-owner approve of the murder of another slave-owner. Slaves were considered to be property as were gladiators, not real people, like members of another tribe were considered to be more physical threats than fellow humans.

The examples you are giving highlight, as I said above, the evolution of our understanding of morality, not of morality itself. In 1,000 years, lying, cheating, stealing, rape and murder will still be immoral.