The popular concept–that we should each determine our own morality–is based on the belief that the spiritual realm is nothing at all like the rest of the world. Does anyone really believe that? For many years after each of the morning and evening Sunday services I remained in the auditorium for another hour to field questions. Hundreds of people stayed for the give-and-take discussions. One of the most frequent statements I heard was that 'Every person has to define right and wrong for him- or herself.' I always responded to the speakers by asking, 'Is there anyone in the world right now doing things you believe they should stop doing no matter what they personally believe about the correctness of their behavior?' They would invariable say, 'Yes, of course.' Then I would ask, “Doesn’t that mean that you do believe there is some kind of moral reality that is "there" that is not defined by us, that must be abided by regardless of what a person feels or thinks?' Almost always, the response to that question was silence, either a thoughtful or a grumpy one.
Timothy J. Keller, The Reason for God: Belief in an Age of Skepticism
morality, postmodernism