And anyway how do I know that my god is good in the first place? According to the Gnostics, God, the Creator of earth, was evil. So, for Gnostics, it would be bad to follow the laws of the god worshipped by the Jews, Christians and Muslims. And what about Buddhism? Why should I believe that Buddha knew what ‘good’ was? Why accept his definition of good and not someone else’s? Regarding Hinduism, why should I buy into the particular view of good promoted in the Hindu holy books? Why not choose someone else’s holy books? And what if my god had a rather different moral compass from the one we’re accustomed to. If I were a Nazi who ‘believed’ in Hitler, I would conclude that it was ‘good’ to kill Jews. Why? Because my god said so, and it’s incumbent upon us to obey our god.
A former Archbishop of Canterbury said that he supported smacking children to teach them the difference between right and wrong. In fact all he was actually doing was promoting a Pavlovian view that our behaviour should be conditioned by a schedule of reward and punishment. There’s no connection at all with right and wrong. Hitler rewarded children for hating Jews, and punished them if they didn’t. Would the Archbishop still agree with the smacking route to ‘goodness’ if this were the outcome?
And what about Nietzsche? He said that the concept of ‘good’ evolved from a patrician notion in Ancient Rome to a plebeian one in the ‘slave morality’ of Christianity. The idea that 'good' evolves (and all the evidence supports Nietzsche), fatally undermines any possibility of an absolute definition of good.
If I modified the original question to ‘why should I pretend to be good?’ would most people’s answers to the original be significantly different? Probably not. What does that tell us?
