Some really fast comments on the Pascal's Mugging part:

1) For ordinary x-risk scenarios, the Hansonian inverse-impact adjustment for "you're unlikely to have a large impact" is within conceivable reach of the evidence - if the scenario has you affecting 10^50 lives in a future civilization, that's just 166 bits of evidence required.

2) Of course, if you're going to take a prior of 10^-50 at face value, you had better not start spouting deep wisdom about expert overconfidence when it comes to interpreting the likelihood ratios - only invoking "expert overconfidence" on one kind of extreme probability really is a recipe for being completely oblivious to the facts.

3) The Hansonian adjustment starts out by adding up to expected value ratios around 1 - it says that based on your priors, all scenarios that put you in a unique position to affect different large numbers of people in the same per-person way will have around the same expected value. Evidence then modifies this. If Pascal's Mugger shows you evidence with a million-to-one Bayesian likelihood ratio favoring the scenario where they're a Matrix Lord who has put you in a situation to affect 3^^^3 lives, the upshot is that you treat your actions as having the power to affect a million lives. It's exactly the same if they say 4^^^^4 lives are at stake. It's an interesting question as to whether this makes sense. I'm not sure it does.

4) But the way the Hansonian adjustment actually works out (the background theory that actually implements it in a case like this) is that after seeing medium amounts of evidence favoring the would-be x-risk charity, the most likely Hanson-adjusted hypothesis then becomes the non-Bayesian-disprovable scenario that rather than being in one of those amazingly unique pre-Singularity civilizations that can actually affect huge numbers of descendants, you're probably in an ancestor simulation instead; or rather, most copies of you are in ancestor simulations and your average impact is correspondingly diluted. Holden Karnofsky would probably not endorse this statement, and to be coherent should also reject the Hansonian adjustment.

5) The actual policy recommendation we get out of the Hansonian adjustment is not for people to be skeptical of the prima facie causal mechanics of existential risk reduction efforts. The policy recommendation we get is that you're probably in a simulation instead, whereupon UDT says that the correct utilitarian policy is for everyone to, without updating on the circumstances of their own existence, try to think through a priori what sort of ancestor simulations they would expect to exist and which parts of the simulation would be of most interest to the simulator (and hence simulated in the greatest detail with largest amount of computing power expended on simulating many slightly different variants), and then expend extra resources on policies that would, if implemented across both real and simulated worlds, make the most intensely simulated part of ancestor simulations pleasant for the people involved. A truly effective charity should spend money on nicer accommodations and higher-quality meals for decision theory conferences, or better yet, seek out people who have already led very happy lives and convince them to work on decision theory. Holden would probably not endorse this either.