So the idea is that 21st century American and caveman Gork from 40000 BC probably have very similar preference, because they have very similar cognitive architecture
If something like Julian Jaynes' notion of a recent historical origin of consciousness from a prior state of bicameralism is true, we might be in trouble there.
More generally, you need to argue that culture is a negligible part of cognitive architecture; I strongly doubt that is the case.
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?