You’re going to put your trust in 12 random jurors from the street whose only common qualification is that they all were unable to somehow get out of unwillingly serving on a jury? How often does a CEO or CFO or CIO or Chairman or board member of a Fortune 1000 company or a S&P 500 company serve on a jury? No, the jury system is heavy laden with the homeless and unemployed and underemployed who don’t have nearly as much to lose financially being paid $40 a day for a week or two weeks of potentially losing their regular job income for that period. And other jurors (who did unsuccessfully try to get out of jury duty) who want to get away from the jury ASAP back to a job paying more than $40 a day, and if that means just voting guilty to get home quicker rather than deliberate longer, even though they might not be convinced of guilt, then so be it. No sweat off his back if an innocent man spends the next 5, 10 or 20 years languishing in prison.
And judges who if they woke up on the wrong side of the bed that morning or missed breakfast or are hungry for lunch or don’t like your lawyer or are good friends with the prosecutor can easily and subtly push for a conviction by all kinds of unjust rulings against the defendant.
Or a system that frequently and regularly uses convicts in plea bargains who are promised a much lower jail sentence if they testify against the defendant, and will comply and will make make up whatever it takes to make the prosecutor happy and get that lower jail sentence by falsely testifying or by turning in innocent people so that he has someone to testify against in exchange for an easier sentence.
In Beis Din a convict is pasul l’eidus for very good reason.
And prosecutors who must run for re-election by getting convictions and proving to dumb voters how tough on crime they are or are seeking appointment to higher office in the DOJ or future elected office by making a name for themselves and pandering to the cameras and needing bodies to convict.
One nice perk of being a prosector is giving the perp walk to those “innocent until proven guilty”, and calling up all the TV stations beforehand (“on the condition of anonymity”) to give them the addresses the FBI will raid to take those non-convicted out in handcuffs in front of their children and neighbors.