It's not just CEV and recursive self-modification, either. CEV only works on individuals and (many) individuals will FOOM once they acquire FAI. If individuals don't FOOM into FAI's (and I see no reason that they would choose to do so) we need a fully general moral/political theory that individuals can use to cooperate in a post-singularity world. How does ownership work when individuals suddenly have the ability to manipulate matter and energy on much greater scales than even governments can today? Can individuals clone themselves in unlimited number? Who actually owns solar and interstellar resources? I may trust a FAI to implement CEV for an individual but I don't necessarily trust it to implement a fair universal political system; that's asking me to put too much faith in a process that won't have sufficient input until it's too late. If every individual FOOMed at the same rate perhaps CEV could be used over all of humanity to derive a fair political system, but that situation seems highly unlikely. The most advanced individuals will want and need the most obscure and strange sounding things and current humans will simply be unable to fully evaluate their requests and the implications of agreeing to them.