IMO, the "rapid takeoff" idea should probably be seen as a fundraising ploy. It's big, scary, and it could conceivably happen - just the kind of thing for stimulating donations.
It seems that SIAI would have more effective methods for fundraising, e.g. simply capitalizing on "Rah Singularity!". I therefore find this objection somewhat implausible.
Many people complain that the Singularity Institute's "Big Scary Idea" (AGI leads to catastrophe by default) has not been argued for with the clarity of, say, Chalmers' argument for the singularity. The idea would be to make explicit what the premise-and-inference structure of the argument is, and then argue about the strength of those premises and inferences.
Here is one way you could construe one version of the argument for the Singularity Institute's "Big Scary Idea":
Cool. Glad this turned out to be helpful.
A recent study by folks at the Oxford Centre for Neuroethics suggests that Greene et. al.'s results are better explained by appeal to differences in how intuitive/counterintuitive a moral judgment is, rather than differences in how utilitarian/deontological it is. I had a look at the study, and it seems reasonably legit, but I don't have any expertise in neuroscience. As I understand it, their findings suggest that the "more cognitive" part of the brain gets recruited more when making a counterintuitive moral judgment, whether utilitarian or deontological.
Also, it is worth noting that attempts to replicate the differences in response times have failed (this was the result with the Oxford Center... (read more)
A simple explanation is that using phrases like "brain scans indicate" and including brain scan images signals scientific eliteness, and halo effect/ordinary reasoning causes them to increase their estimate of the quality of the reasoning they see.
Best rejection therapy ever.
Do you know about Giving What We Can? You may be interested in getting to know people in that community. Basically, it's a group of people that pledges to give 10% of their earnings to the most effective charities in the developing world. Feel free to PM me or reply if you want to know more.
Usually, average utilitarians are interested in maximizing the average well-being of all the people that ever exist, they are not fundamentally interested in the average well-being of the people alive at particular points of time. Since some people have already existed, this is only a technical problem for average utilitarianism (and a problem that could not even possibly affect anyone's decision).
Incidentally, not distinguishing between averages over all the people that ever exist and all the people that exist at some time leads some people to wrongly conclude that average utilitarianism favors killing off people who are happy, but less happy than average.
Gustaf Arrhenius is the main person to look at on this topic. His website is here. Check out ch. 10-11 of his dissertation Future Generations: A Challenge for Moral Theory (though he has a forthcoming book that will make that obsolete). You may find more papers on his website. Look at the papers that contain the words "impossibility theorem" in the title.
Both you and Eliezer seem to be replying to this argument:
People only intrinsically desire pleasure.
An FAI should maximize whatever people intrinsically desire.
Therefore, an FAI should maximize pleasure.
I am convinced that this argument fails for the reasons you cite. But who is making that argument? Is this supposed to be the best argument for hedonistic utilitarianism?
I prefer this briefer formalization, since it avoids some of the vagueness of "adequate preparations" and makes premise (6) clearer.