What I meant is: I encourage people to behave rationally by believing X, and would like them to further encourage others.
Either you have a way to actually get most people to believe in X, or the jury system fails in that respect.
There's also room for bias in the selection of the reference class used. (All the numbers that follow are random.) A long-haired blonde man is brought to trial. On the one hand, men are 10% more likely than average to commit violent crime. But on the other hand blonde men are 13% less likely than average. But then, this is a truck driver, and they're 25% more likely than average. But then, he grew up in Boston, and only 37% of accused Bostonites are convicted. But then...
"of blacks brought to jury trial, they're X% likely to be guilty on average"
To be precise, they're X% more likely to be found guilty on average. Which is not the same, in a relevant way.
Suppose you think there's unfair bias against long-haired people in the courts today. If you use today's statistics for conviction % of long-hairs accused, then you may perpetuate that bias. But where else do you get your prior?
I definitely don't think the method of picking a single reference class is a good one. Many overlapping big and small classes aren't a problem if you reason correctly.
Re: what if conviction rates are drastically unfair? That's a good point. It's definitely possible to prove that some people who were convicted are likely innocent (but not all of them, just those with e.g. exonerating DNA evidence). I suppose I assumed that the false-guilty rate in the US is less than 10%, but knowing that the false guilty for some privileged class (let's say attractive ...
The following will explore a couple of areas in which I feel that the criminal justice system of many Western countries might be deficient, from the standpoint of rationality. I am very much interested to know your thoughts on these and other questions of the law, as far as they relate to rational considerations.
Moral Luck
Moral luck refers to the phenomenon in which behaviour by an agent is adjudged differently based on factors outside the agent's control.
Suppose that Alice and Yelena, on opposite ends of town, drive home drunk from the bar, and both dazedly speed through a red light, unaware of their surroundings. Yelena gets through nonetheless, but Alice hits a young pedestrian, killing him instantly. Alice is liable to be tried for manslaughter or some similar charge; Yelena, if she is caught, will only receive the drunk driving charge and lose her license.
Raymond, a day after finding out that his ex is now in a relationship with Pardip, accosts Pardip at his home and attempts to stab him in the chest; Pardip smashes a piece of crockery over Raymond's head, knocking him unconscious. Raymond is convicted of attempted murder, receiving typically 3-5 years chez nous (in Canada). If he had succeeded, he would have received a life sentence, with parole in 10-25 years.
Why should Alice be punished by the law and demonized by the public so much more than Yelena, when their actions were identical, differing only by the sheerest accident? Why should Raymond receive a lighter sentence for being an unsuccessful murderer?
Some prima facie plausible justifications:
Trial by Jury; Trial by Judge
Those of us who like classic films may remember 12 Angry Men (1957) with Henry Fonda. This was a remarkably good film about a jury deliberating on the murder trial of a poor young man from a bad neighbourhood, accused of killing his father. It portrays the indifference (one juror wants to be out in time for the baseball game), prejudice and conformity of many of the jurors, and how this is overcome by one man of integrity who decides to insist on a thorough look through the evidence and testimony.
I do not wish to generalize from fictional examples; however, such factors are manifestly at play in real trials, in which Henry Fonda cannot necessarily be relied upon to save the day.
Komponisto has written on the Knox case, in which an Italian jury came to a very questionable (to put it mildly) conclusion based on the evidence presented to them; other examples will doubtless spring to mind (a famous one in this neck of the woods is the Stephen Truscott case - the evidence against Truscott being entirely circumstantial.
More information on trial by jury and its limitations may be found here. Recently the UK has made some moves to trial by judge for certain cases, specifically fraud cases in which jury tampering is a problem.
The justifications cited for trial by jury typically include the egalitarian nature of the practice, in which it can be guaranteed that those making final legal decisions do not form a special class over and above the ordinary citizens whose lives they effect.
A heartening example of this was mentioned in Thomas Levenson's fascinating book Newton and the Counterfeiter. Being sent to Newgate gaol was, infamously in the 17th and 18th centuries, an effective death sentence in and of itself; moreover, a surprisingly large number of crimes at this time were capital crimes (the counterfeiter whom Newton eventually convicted was hanged). In this climate of harsh punishment, juries typically only returned guilty verdicts either when evidence was extremely convincing or when the crime was especially heinous. Effectively, they counteracted the harshness of the legal system by upping the burden of proof for relatively minor crimes.
So juries sometimes provide a safeguard against abuse of justice by elites. However, is this price for democratizing justice too high, given the ease with which citizens naive about the Dark Arts may be manipulated? (Of course, judges are by no means perfect Bayesians either; however, I would expect them to be significantly less gullible.)
Are there any other systems that might be tried, besides these canonical two? What about the question of representation? Does the adversarial system, in which two sides are represented by advocates charged with defending their interests, conduce well to truth and justice, or is there a better alternative? For any alternatives you might consider: are they naive or savvy about human nature? What is the normative role of punishment, exactly?
How would the justice system look if LessWrong had to rewrite it from scratch?