UFAI is not strongly motivated to sim us in large numbers
This is the weakest assumption in your chain of reasoning. Design space for UFAI is far bigger than for FAI, and we can't make strong assumptions about what it is or is not motivated to do -- there are lots of ways for Friendliness to fail that don't involve paperclips.
This is the weakest assumption in your chain of reasoning. Design space for UFAI is far bigger than for FAI,
Irrelevant. The design space of all programs is infinite - do you somehow think that the set of programs that humans create is a random sample from the set of all programs?. The size of the design space has absolutely nothing whatsoever to do with any realistic actual probability distribution over that space.
we can't make strong assumptions about what it is or is not motivated to do
Of course we can - because UFAI is defined as superintelligence that doesn't care about humans!
At some point soon, I'm going to attempt to steelman the position of those who reject the AI risk thesis, to see if it can be made solid. Here, I'm just asking if people can link to the most convincing arguments they've found against AI risk.
EDIT: Thanks for all the contribution! Keep them coming...