Andreas Mogensen, a Senior Research Fellow at the Global Priorities Institute, has just published a draft of a paper on "Maximal Cluelessness". Abstract:
I argue that many of the priority rankings that have been proposed by effective altruists seem to be in tension with apparently reasonable assumptions about the rational pursuit of our aims in the face of uncertainty. The particular issue on which I focus arises from recognition of the overwhelming importance and inscrutability of the indirect effects of our actions, conjoined with the plausibility of a permissive decision principle governing cases of deep uncertainty, known as the maximality rule. I conclude that we lack a compelling decision theory that is consistent with a long-termist perspective and does not downplay the depth of our uncertainty while supporting orthodox effective altruist conclusions about cause prioritization.
When I said "I think both of these "stories" I've told are extremely unlikely, and for practical purposes aren't worth bearing in mind", the bolded bit meant that I think a person will tend to better achieve their goals (including altruistic ones) if they don't devote explicit attention to such (extremely unlikely) "stories" when making decisions. The reason is essentially that one could generate huge numbers of such stories for basically every decision. If one tried to explicitly think through and weigh up all such stories in all such decision situations, one would probably become paralysed.
So I think the expected value of making decisions before and without thinking through such stories is higher than the expected value of trying to think through such stories before making decisions.
In other words, the value of information one would be expected to get from spending extra time thinking through such stories is probably usually lower than the opportunity cost of gaining that information (e.g., what one could've done with that time otherwise).