Value drift is a real-world phenomenon, something that happens to humans. No real-world phenomenon can be bad "by definition" - our morality is part of reality and cannot be affected by the sympathetic magic of dictionaries. Maybe you're using "value drift" in a non-traditional sense, as referring to some part of your math formalism, instead of the thing that happens to humans?
No real-world phenomenon can be bad "by definition"
By definition, as in the property is logically deduced (given some necessary and not unreasonable assumptions). Consider a bucket with 20 apples of at least 100 grams each. Such buckets exist, they are "real-world phenomena". Its weight is at least 2 kg "by definition" in the same sense as misoptimized future is worse than optimized future.
Ben Goertzel:
Robin Hanson:
We all know the problem with deathism: a strong belief that death is almost impossible to avoid, clashing with undesirability of the outcome, leads people to rationalize either the illusory nature of death (afterlife memes), or desirability of death (deathism proper). But of course the claims are separate, and shouldn't influence each other.
Change in values of the future agents, however sudden of gradual, means that the Future (the whole freackin' Future!) won't be optimized according to our values, won't be anywhere as good as it could've been otherwise. It's easier to see a sudden change as morally relevant, and easier to rationalize gradual development as morally "business as usual", but if we look at the end result, the risks of value drift are the same. And it is difficult to make it so that the future is optimized: to stop uncontrolled "evolution" of value (value drift) or recover more of astronomical waste.
Regardless of difficulty of the challenge, it's NOT OK to lose the Future. The loss might prove impossible to avert, but still it's not OK, the value judgment cares not for feasibility of its desire. Let's not succumb to the deathist pattern and lose the battle before it's done. Have the courage and rationality to admit that the loss is real, even if it's too great for mere human emotions to express.