The very opposite of this hypothesis is actually more likely to be true. Kuru is a manifestation of this same prion disease (PRNP gene variant disease) that is essentially only found in people from New Guinea who practiced a form of cannibalism in which they ate the brains of dead people as part of a funeral ritual.
This is exactly the wrong interpretation. We know that cannibalism causes prion disease, and we have known that for as long as we have known about prion disease. the question is not whether cannibalism causes prion disease, which it definitely does, but whether past cannibalism was common enough to have selected for some innate resistance to it.
Like you said, we know that cannibalism causes prion disease. We know this. Thus, we are not resistant to it. So from an evolutionary perspective you could make a strong argument that what actually happened was that those humans who didn't engage in cannibalism and die of prion disease were heavily selected for. Which is probably why you don't see many humans eating the dead. Now that last bit is speculation, but all this is speculation. But based on my own introspection, I'm imagining myself stumbling upon a recently dead human corpse, I'm almost certain my innate reaction -- (well, almost surely innate, and not socialized, since I've never been explicitly taught how to react in such a situation) -- is that I'm definitely not going to fucking eat that corpse. In fact, the only humans that do seem to still engage in cannibalism do it out of some social ritual.
the prevalence of the PNRP gene is much better explained by periods of time when humans were very cannibalistic. This makes more sense behaviorally as well, since humans are very difficult to program with instincts. I would bet dollars to donuts that the average hunter gatherer/early farmer had no such revulsion. Meat is meat.
Well here is the major point: there is only one prion (PRNP), for which all mammals seem to be susceptible to disease. It would be odd if deer and sheep had coevolved the same resistances and susceptibility to PRNP due to human cannibalism
