Why does Robertson, or anyone else, insist on moral realism? And what exactly does he mean by it?
There seem to be different usages of "moral realism", which is confusing. The main two are:
Morals are an objective property of the universe, or possibly of mathematics (e.g. game theoretic cooperation), which can be deduced and agreed on, even separately from purely human concerns and attributes. So we can speak of objective morals. And if one believes that humans are typical of (evolved) intelligences, and that evolution removes behavior that is self-destructive or unstable, it's likely that common human morals are somewhat correlated with these universal morals.
Humans are very homogenous compared to all possible intelligent agents. Human moral beliefs, intuitions and actions are more alike than they are different. This shared core is objective or "real" in the sense that it is independent of any particular human or even any particular human culture. So we can speak of objective human!morals.
Well, Robertson insists on moral realism because he is a believing Christian and Christianity is rather insistent about it -- specifically in the sense of your first usage case.
I haven't seen anyone call the second case "moral realism" outside of the LW context.
Link to Blog Post: "Extremism in Thought Experiments is No Vice"
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