Are witness to the objective nature of morality:
"The discordance over moral codes witnesses to the fact of moral experience. You cannot quarrel about unknown elements. The basis of every discord is some common experience, discordantly realized." -- Alfred North Whitehead, The Function of Reason, p. 86
This is very reminiscent of Wittgenstein's point that we can only disagree on a matter upon which we largely agree. For instance, one of the readers of this blog can refer to me as a "retard" on property rights only because we largely agree as to what property rights are. If I thought property rights were flying purple snakes that lived in my dreams, we would simply be talking about completely different things, and not disagreeing about the same thing.