Taken from some old comments of mine that never did get a satisfactory answer.
1) One of the justifications for CEV was that extrapolating from an American in the 21st century and from Archimedes of Syracuse should give similar results. This seems to assume that change in human values over time is mostly "progress" rather than drift. Do we have any evidence for that, except saying that our modern values are "good" according to themselves, so whatever historical process led to them must have been "progress"?
2) How can anyone sincerely want to build an AI that fulfills anything except their own current, personal volition? If Eliezer wants the the AI to look at humanity and infer its best wishes for the future, why can't he task it with looking at himself and inferring his best idea to fulfill humanity's wishes? Why must this particular thing be spelled out in a document like CEV and not left to the mysterious magic of "intelligence", and what other such things are there?
Right - but this seems as though it isn't how things are likely to go down. CEV is a pie-in-the-sky wishlist - not an engineering proposal. Those attempting to directly implement things like it seem practically guaranteed to get to the plate last. For example Ben's related proposal involved "non-invasive" scanning of the human brain. That just isn't technology we will get before we have sophisticated machine intelligence, I figure. So: either the proposals will be adjusted so they are more practical en route - or else, the proponents will just fail.
Most likely there will be an extended stage where people tell the machines what to do - much as Asimov suggested. The machines will "extrapolate" in much the same way that Google Instant "extrapolates" - and the human wishes will "cohere" - to the extent that large-scale measures in society encourage cooperation.