Basically a non-cognitivist, then.
It is generally more beneficial for the spreading of our seed to work in groups for survival. We are not terribly strong animals.
Sometimes it is more beneficial for one man’s seed to transgress against his fellows.
This will generally not be tolerated by the rest of the community.
This is how systems of governance are created.
As was stated above, moral systems are entirely subjective (i.e. the sociopath), but they are made better and more consistent through a system of trial-and-error on the part of generations.
(I just watched a What Would You Do this evening that showed people being shown a horrible product, and noone would speak up until someone else did. An interesting coincedence