You'd have thought it wouldn't be the proteins in the input, but the prions in the output they would care about. They're remarkably resilient, it's not unreasonable to be cautious.
Or at least focus on not having neural tissue in the input. That wouldn't rely come from consumer waste, would it?
Agreed, this is one area where care should be taken. The effects of CJD are absolutely horrendous, and it’s easy to imagine that this might be a way to transmit it.