Why would CEV operate on humans that do exist, and not on humans that could exist?
To do the latter, you would need a definition of "human" that can not just distinguish existing humans from existing non-humans, but also pick out all human minds from the space of all possible minds. I don't see how to specify this definition. (Is this problem not obvious to everyone else?)
For example, we might specify a prototypical human mind, and say that "human" is any mind which is less than a certain distance from the prototypical mind in design space. But then the CEV of this "humankind" is entirely dependent on the prototype that we pick. If the FAI designers are allowed to just pick any prototype they want, they can make the CEV of "humanity" come out however they wish, so they might as well have the FAI use the CEV of themselves. If they pick the prototype by taking the average of all existing humans, then that allows the same attack described in my post.
The problem is indeed there, but if the goal is to find out the human coherent extrapolated volition, then a definition of human is necessary.
If we have no way of picking out human minds from the space of all possible minds, then we don't really know what we're optimizing for. We can't rule out the possibility that a human mind will come into existence that will not be (perfectly) happy with the way things turn out.* This may well be an inherent problem in CEV. If FAI will prevent such humans from coming into existence, then it has in effect enforced its o...
It’s the year 2045, and Dr. Evil and the Singularity Institute have been in a long and grueling race to be the first to achieve machine intelligence, thereby controlling the course of the Singularity and the fate of the universe. Unfortunately for Dr. Evil, SIAI is ahead in the game. Its Friendly AI is undergoing final testing, and Coherent Extrapolated Volition is scheduled to begin in a week. Dr. Evil learns of this news, but there’s not much he can do, or so it seems. He has succeeded in developing brain scanning and emulation technology, but the emulation speed is still way too slow to be competitive.
There is no way to catch up with SIAI's superior technology in time, but Dr. Evil suddenly realizes that maybe he doesn’t have to. CEV is supposed to give equal weighting to all of humanity, and surely uploads count as human. If he had enough storage space, he could simply upload himself, and then make a trillion copies of the upload. The rest of humanity would end up with less than 1% weight in CEV. Not perfect, but he could live with that. Unfortunately he only has enough storage for a few hundred uploads. What to do…
Ah ha, compression! A trillion identical copies of an object would compress down to be only a little bit larger than one copy. But would CEV count compressed identical copies to be separate individuals? Maybe, maybe not. To be sure, Dr. Evil gives each copy a unique experience before adding it to the giant compressed archive. Since they still share almost all of the same information, a trillion copies, after compression, just manages to fit inside the available space.
Now Dr. Evil sits back and relaxes. Come next week, the Singularity Institute and rest of humanity are in for a rather rude surprise!