The assumption that all humans foom, AND all do so at the same time, AND all do so at the same (or insignificant difference) rate, AND (Remain Safe under self-modification OR never find a way to self-modify), AND are human-Friendly by default... is a very far-fetched combined assumption to be making here, IMO.

The assumptions that I make are that the humanity-fooming would be both very slow, and generally available in some way (I'm not sure entirely how, but brain-computer interfaces are a possibility). That all humans foom, at more-or-less the same time, and at more-or-less the same rate, then follows on (especially in the case of the brain-computer interface, in which case the speed of the foom is controlled by the speed of technological development).

I don't think that all of the fooming people would be Friendly, but I do think that under those circumstances, any Unfriendly ones would be outnumbered by roughly-equivalently-intelligent Friendly ones, resulting in a by-and-large Friendly consensus.