If a person accepts the standard view of moral theories that morality always provides a unique correct answer to every moral question about how one morally ought to act, then all moral disagreements must be explained away. Those who disagree must be not equally informed, not impartial, or not rational. If two people who hold the standard view are discussing a controversial moral issue and disagree with each other, they must regard the other as ignorant, partial, or irrational. These are not the attitudes that make for a respectful and fruitful discussion of a controversial moral issue. However, if both hold the view that morality does not always provide unique correct answers to moral questions, then they may conclude, usually correctly, that this is one of these issues. Then they need not regard the other person's view as morally unacceptable and can cooperate in trying to find out the source of their disagreement.
(Bernard Gert, Common Morality: Deciding What to Do [New York: Oxford University Press, 2004], 145-6)
