Hey I'm a big fan of C.S. Lewis and agree with his views. I'm reading 'Mere Christianity' now and i just have this problem with the Law of Nature. Remember, i think he's a genius and hence i think he's right; so I'd love someone to blow this query out of the water.
I think he states that this 'standard' is ingrained in all (or most) of us, that we cannot get rid of it. This standard we all have he says must have been given to us by some other mind or being which is God. The problem i have is this: Could we not find or create this standard ourselves by simply putting ourselves in others shoes and treating others how we would like to be treated?