A comment to http://singinst.org/blog/2010/10/27/presentation-by-joshua-foxcarl-shulman-at-ecap-2010-super-intelligence-does-not-imply-benevolence/: Given as in the naive reinforcement learning framework (and that can approximate some more complex notions of value) that the value is in the environment, you don't want to be too hasty with the environment lest you destroy a higher value you haven't yet discovered! So you especially wouldn't replace high complexity systems like humans with low entropy systems like computer chips, without first analyzing them.
I was thinking about the former type, which is indeed more like freezing. However, it is unlikely that an unFriendly AI would ever re-implement humanity (especially if it mostly cares about entropy), so it's practically akin to killing.