Time travel is fiction, moral relativism is about dealing with the real. Personally, I read fiction.
Same issue with omniscience. While some people claim that for their personal dieties, it still doesn't make them personally omniscient. Once again, it's about taking responsibility and actually actively making judgement calls. Omniscience is another fiction.
I was watching the documentary about the making of the first The Lord of The Rings movie last night, and the discussion on there about Tolkien's concept of evil: in particular the concept of "monism" (one "right" way) and "wraithing". Wraithing in particular is of interest because we see that in our societies, bureaucracies, armed forces where evil is committed by people "just following orders."
So fiction is one way of exploring these very concepts.