There's a deeper question here: ideally, we would like our CEV to make choices for us that aren't our choices. We would like our CEV to give us the potential for growth, and not to burden us with a powerful optimization engine driven by our childish foolishness.
One obvious way to solve the problem you raise is to treat 'modifying your current value approximation'' as an object-level action by the AI, and one that requires it to compute your current EV - meaning that, if the logical consequences of the change (including all the future changes that the AI predicts will result from that change) don't look palatable to you, the AI won't make the first change. In other words, the AI will never assign you a value set that you find objectionable right now. This is safe in some sense, but not ideal. The profoundly racist will never accept a version of their values which, because of its exposure to more data and fewer cognitive biases, isn't racist. Ditto for the devoutly religious. This model of CEV doesn't offer the opportunity for growth.
It might be wise to compromise by locking the maximum number of edges in the graph between you and your EV to some small number, like two or three - a small enough number that value drift can't take you somewhere horrifying, but not so tightly bound up that things can never change. If your CEV says it's okay under this schema, then you can increase or decrease that number later.
Yes, CEV is a slippery slope. We should make sure to be as aware of possible consequences as practical, before making the first step. But CEV is the kind of slippery slope intended to go "upwards", in the direction of greater good and less biased morals. In the hands of superintelligence, I expect CEV to extrapolate values beyond "weird", to "outright alien" or "utterly incomprehensible" very fast. (Abandoning Friendliness on the way, for something less incompatible with The Basic AI Drives. But that is for completel...
My main objection to Coherent Extrapolated Volition (CEV) is the "Extrapolated" part. I don't see any reason to trust the extrapolated volition of humanity - but this isn't just for self centred reasons. I don't see any reason to trust my own extrapolated volition. I think it's perfectly possible that my extrapolated volition would follow some scenario like this:
There are many other ways this could go, maybe ending up as a negative utilitarian or completely indifferent, but that's enough to give the flavour. You might trust the person you want to be, to do the right things. But you can't trust them to want to be the right person - especially several levels in (compare with the argument in this post, and my very old chaining god idea). I'm not claiming that such a value drift is inevitable, just that it's possible - and so I'd want my initial values to dominate when there is a large conflict.
Nor do I give Armstrong 7's values any credit for having originated from mine. Under torture, I'm pretty sure I could be made to accept any system of values whatsoever; there are other ways that would provably alter my values, so I don't see any reason to privilege Armstrong 7's values in this way.
"But," says the objecting strawman, "this is completely different! Armstrong 7's values are the ones that you would reach by following the path you would want to follow anyway! That's where you would get to, if you started out wanting to be more altruistic, had control over you own motivational structure, and grew and learnt and knew more!"
"Thanks for pointing that out," I respond, "now that I know where that ends up, I must make sure to change the path I would want to follow! I'm not sure whether I shouldn't be more altruistic, or avoid touching my motivational structure, or not want to grow or learn or know more. Those all sound pretty good, but if they end up at Armstrong 7, something's going to have to give."