Then it is a matter of degree: there is a lot of regularity to our moral instincts. But to attack the idea that there are objective moral truths out there it is enough to see that our intuitions do not fit any one great moral principle.
I suppose you could extract one particular regularity—such as “minmize total harm” and call that the objective moral truth. But then someone else will extract some other, distinct regularity such as “never use a person merely as a means” (the golden rule) and call that the objective moral truth. And they contradict each other.
Then it is a matter of degree: there is a lot of regularity to our moral instincts. But to attack the idea that there are objective moral truths out there it is enough to see that our intuitions do not fit any one great moral principle.
I suppose you could extract one particular regularity—such as “minmize total harm” and call that the objective moral truth. But then someone else will extract some other, distinct regularity such as “never use a person merely as a means” (the golden rule) and call that the objective moral truth. And they contradict each other.