But that's not a hit against decision theory. That's a hit against bad utility functions.

We know from Eliezer's writings that almost any strong goal-directed chessplayer AI will destroy the world. Well guess what, if a non-world-destroying utility function appears almost impossibly hard to formulate, in my book it counts as a hit against the concept of utility functions. Especially seeing as machines based on e.g. control theory (RichardKennaway) behave much more sensibly - they almost never display any urge to screw up the whole world, instead being content to sit there and tweak their needle.