The disagreements I was talking about - which I clam are many, perhaps most, disagreements - are not about unknown or disputed facts, but about conflicting values and goals. Such disagreements can't be resolved into sides being objectively right or wrong (unless you're a moral realist). If you side with one of the sides, that's the same as saying their desires are 'right' to you, and implementing their desires usually (in most moral theories in practice) outweighs the cost of the moral outrage suffered by those who disagree. (E.g., I would want to free one slave even if it made a million slave-owners really angry, very slightly increasing the incidence of heart attacks and costing more QALYs in aggregate than the one slave gained.)