SteakNPotatoes
There is no absolute authority for morality. Each society has it’s own concept of what is moral, and that can (and does) change over time.
A mere 400 years ago it was acceptable to kill those who did not hold the same religious ideas as the rest of the community. That is now regarded as immoral.
A mere 300 years ago it was perfectly acceptable to regard another human being as property. That is now regarded as immoral.
I’m afraid this line of reasoning, relativistic as it is, was predictable.
You are confused by the notion that the true moral law changes from one generation to the next. It does not. People may declare the law has been changed, but that doesn’t make it so.
The Ten Commandments of Moses are still in force. The two Great Commandments of Jesus are still in force. They have not been overturned by time or circumstances.
People who refuse to obey those laws do so at their own risk. Those people include Popes and Bishops who, having lost their moral moorings, may have promoted violence and wars against fellow Christians. They were frail humans, who should have known better.
Hitler, Stalin, and Mao, however, all three atheists, did not even have the benefit of a moral foundation they could violate, since, like good atheists, they acknowledged no fixed foundation at all. That is why the murderous cruelties reflected in the Crusades and the Inquisitions and the Wars of the Reformation look more like a warm-up act compared to the full scale holocausts of the 20th Century.