Moral disagreements are factual disagreements
"Thus we can explain all moral controversy and progress. For when we try to argue that someone is wrong about a moral proposition we always find ourselves arguing in either of two ways: either we point out how their understanding of the facts is wrong, or we point out how they have deduced the incorrect values from the actual facts. Both can be valid arguments. For instance, we tell the Nazi that his beliefs, like that Jews are not human beings and that they are plotting to take over the world, are factually false, and therefore his morals regarding the Jews are in error"
"In fact, almost every indignity just mentioned can be attributes to an insufficient taste for evidence, to an uncritical faith in one dogma or another."