Robertson is mistaken in believing that atheists all deny the existence of right and wrong. However, from a timeless decision point of view, someone who does in fact deny the existence of right and wrong is at least partly "responsible" for it if he is murdered by someone who does not believe that murder is wrong and who would not have done it if he did believe it was wrong.
Saying he has no responsibility at all in this sense, would be like saying that the person who takes two boxes in a Newcomb situation is not responsible for the fact that he didn't get the million.
Link to Blog Post: "Extremism in Thought Experiments is No Vice"
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This is a LW discussion post for Yvain's blog posts at Slate Star Codex, as per tog's suggestion:
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