> if we are probabilistic systems, we presumably can't actually do things like rationalise, or design things like legal systems.
Why not? Computers can reason and have constructed proofs. Probably a computer could construct legal arguments too. They might have some probability for errors (e.g. cosmic rays) that need to be accounted for and corrected, just like humans.
> But if we want a picture that lets us keep some of our current view of human life, it is not clear that bringing probabilistic systems into the picture helps any.
It might help people understand why people murder, or commit crime. Criminals might have errors that need to be corrected rather than focusing on a crime that needs to be punished.