Morality by Culture?

To improve a society's moral code means that the society changes its laws and values to more closely approximate an external moral ideal.  If no such standard exists, if cultural values are the highest possible law, then there is no way for those standards to be better than what they are at any given moment.  They can only be different.

Francis J. Beckwith and Gregory Koukl, “Relativism: Feet Firmly Planted in Mid-Air,” p.53