The argument is typically countered with "the morality of cultures differ; therefore, morality is not objective, but subjective; therefore, there can be no 'standard, objective' source behind these varying moralities."
I found it interesting to read this very counter-argument online against Lewis' argument in Mere C., despite the fact Lewis already anticipated it!
Here then is the quote, and the Q for D is whether it answers the criticism that "morality is not objective, because cultures vary on their moralities".
The quote follows the assertion that "different ages have had quite different moralities".
Has Lewis successfully dealt with the objection against "objective morality" which was based on supposed "differing moralities"? Is there, in fact, a reducible principle that underlies all supposedly differing moralities?But this is not true. There have been differences between their moralities, but these have never amounted to anything like a total difference. If anyone will take the trouble to compare the moral teaching of, say, the ancient Egyptians, Babylonians, Hindus, Chinese, Greeks and Romans, what will really strike him will be how very like they are to each other and to our own. Some of the evidence for this I have put together in the appendix of another book called The Abolition of Man;but for our present purpose I need only ask the reader to think what a totally different morality would mean. Think of a country where people were admired for running away in battle, or where a man felt proud of double-crossing all the people who had been kindest to him. You might just as well try to imagine a country where two and two made five. Men have differed as regards what people you ought to be unselfish to—whether it was only your own family, or your fellow countrymen, or everyone. But they have always agreed that you ought not to put yourself first. Selfishness has never been admired. Men have differed as to whether you should have one wife or four. But they have always agreed that you must not simply have any woman you liked.