Earlier quoted context omitted.
Why was the jury required to understand the law? That's not a reasonable expectation for random people off the street. In the US, juries typically decide questions of _fact_ that are not already agreed upon by both parties (i.e. are in dispute). Judges handle questions of law.
If a fact is known, you don't need the contribution of a random person. If a fact is not known, how can some random person produce it? Out of what. E.g. in the situation of a crime: only activities like crime scene investigation, and interviewing of witnesses can produce anything that can be called a fact. Now so from all that have some collection of real facts from the investigation which do not add up to an absolut…
Yes, it might be better if jurors were all acquainted with Bayesian reasoning and it would definitely be better if things like expert testimony and so forth came with confidence estimates.
And yes, "beyond a reasonable doubt" is pretty qualitative.
My point was that if you are expecting your jurors to have a deep understanding of the law, you are definitely doing it wrong.