You have a personal definition for evil, like everyone else. Many people have definitions of good that include things you see as evil; some of your goals are in conflict. Taking that into account, how can you precommit to implementing the CEV of the whole of humanity when you don't even know for sure what that CEV will evaluate to?
To put this another way: why not extrapolate from you, and maybe from a small group of diverse individuals whom you trust, to get the group's CEV? Why take the CEV of all humanity? Inasmuch as these two CEVs differ, why would you not prefer your own CEV, since it more closely reflects your personal definitions of good and evil?
I don't see how this can be consistent unless you start out with "implementing humanity's CEV" as a toplevel goal, and any divergence from that is slightly evil.
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?