Save 400 lives, with certainty. Save 500 lives, with 90% probability; save no lives, 10% probability.
I'm surprised how few people are reacting to the implausibility of this thought experiment. When not in statistics class, God rarely gives out priors. Probabilities other than 0+epsilon and 1-epsilon tend to come from human scholarship, which is an often imperfect process. It is hard to imagine a non-contrived situation where you would have as much confidence in the 90/10 outcome as in the certain outcome.
Suppose the "90/10" figure comes from cure rates in a study of 20-year-old men, but your 500 patients are mostly middle-aged. You have the choice of disarming a bomb that will kill 400 people with probability 1-epsilon, or of taking that "90/10" estimate, really, really seriously; I know which choice I would make.
Admittedly OT meta-comment: I think Robin Hanson's an interesting thinker, and he has the discipline to self edit that this blog medium seems to require. Eliezer, on the other hand, seems both sophomorically self-impressed and logorrheic. Maybe there are interesting ideas lurking in these posts, but life is entirely too short to read them. Any chance of you guys getting, y'know, separate blogs, since the target audiences appear to be pretty different?