Each of us knows that certain things are wrong—not because we believe they are wrong, but because they really are wrong. And that applies to the moral relativist as well.
If you want to see a relativist sink into a sophistic seizure, ask him about the “virtues” of cruelty, rape, bigotry, exploitation, or the Holocaust. Even the most liberally minded secularist believes such things are wrong, but without a transcendent peg to hang his ethical system, he will be incapable of articulating a coherent moral argument against them. But that could change, if Sam Harris has anything to say.
Harris is a rationalist and trenchant atheist who is highly critical of religion and religious folk. But he is also a moral realist who believes in objective moral truths—truths, he is confident can be grounded in science to form a system of shared moral values.
His argument goes something like this: the natural world operates according to natural laws discoverable through science; morality is a part of the natural world; therefore, morality follows natural laws discoverable through science. …