People have different value structures … not just that they wear different hat

People have different value structures … not just that they wear different hats, but that cultures have fundamentally different understandings of human beings and their interactions and most cultures in the past have dramatically different values than yours. For instance, slavery. It’s part of every state structured culture (meaning cultures with a definable nation, kingdom who are not hunter gatherers) in the world at the time of Columbus — and guess what, whether that slavery is in Asia, Europe, the Americas or Africa all of these cultures believe that slavery is an acceptable and normal condition of life for some people. These cultures also believe and support the idea that the 90% of their populations that were either peasants, servants or slaves should be totally subject to the will, power and brutality of their rulers — so, when a student writes something like “Africans were treated as property and had no say in whether they wanted to be traded and taken to the New World” What can this statement possibly mean? Of course they were treated as property — African and European values told the people of the time that slaves were nothing. So the question of this forum is whether our present gets to dictate what is morally correct — and if it does then why do we get to make that judgement? And why do we make different judgements than cultures did in the past (how come we don’t believe in slavery any more? and don’t say because it is wrong. If it is wrong we are trying to discover what makes us make that choice?)