I think he's making two slightly related points. 1) That while it's possible to talk about moral relativism in the abstract, nobody in their own life is a comp

I think he's making two slightly related points. 1) That while it's possible to talk about moral relativism in the abstract, nobody in their own life is a complete moral relativist, which is to say that they will have _some_ moral system that they live their life by, even if they completely recognize the arbitrariness of it. 2) Moral systems have large degrees of freedom, but they _are_ constrained, and he thinks some of those constraints might be innate. For example, while all forms of violence can be approved of in some society, it's always _conditional_. You could _imagine_ a moral system where arbitrary extreme violence against anyone and anything including yourself and your family would be perfectly moral, but you won't see that in any real society. There are always some conditions under which violence is acceptable.