Because you have stated that they are easily manipulated, fooled, etc. Which means you think their decisions are based little on the truth and evidence presented on the matter and more on their emotional whims and weaknesses.
I believe that you are misrepresenting me, Tinark. What you have in mind is what I wrote in my OP:
"Due process is nothing but an opportunity for the sophists to put on their rhetorical display, to trick the juries, and make a mockery of justice."
There is here no question of juries actually being easily manipulated, deceived, etc. My point was that this is what at least one of the two lawyers is
trying to do. Presumably, one of the lawyers knows that what he's saying doesn't match the evidence. Yet, he's trying to convince the jury of the opposite. He's trying to trick/deceive the jury into believing something that he presumably knows is false.
Are juries actually able to be deceived so easily? Maybe, maybe not. That's not where I was placing my emphasis.
And how does that insure a reduced error rate, more importantly, a reduced error rate in convicting innocent parties?
You ask this as though this should be the sole and primary goal of any criminal justice system. I disagree. The sole and primary goal of any criminal justice system should be the administration of criminal justice. Making sure that innocent parties don't get convicted is part of that, but that's only one factor.
You have in mind the (probably rare) instances in which the police arrest an innocent person.
I have in mind the (probably common) instances in which the police arrest a guilty person, but he either gets off scott free or on a reduced sentence simply because of the way that our criminal justice system works.
Case 1: A man is driving while intoxicated (the man himself admits to being intoxicated while driving, even well after the fact). A policeman pulls him over, determines that he's intoxicated and arrests him. Yet, the man's case ends up being thrown out. Why? Because (so far as I can remember being told), the cop ended up not showing up to court.
Case 2: A guy (for reasons I can't remember) steps out of his vehicle and starts threatening the driver of another vehicle and banging on his window with his hands. The driver therefore pulls out his gun and shows the assailant that he is armed. The assailant flees, calls the police, and reports that somebody just threatened him with a gun. The cop shows up to the scene, interviews both parties, determines the facts of the situation, and tells the guy with the gun that he was perfectly within his rights. The assailant, however? He gets off scott free. No arrest is made, even though he is perfectly guilty of assault (at least). Why? Because the armed driver is only passing through and doesn't want to face the massive inconvenience of showing up to court.
Case 3 (this third is taken from Homicide Hunter): A maintanence man of an apartment lets himself into an apartment, rapes a woman, and then murders both the woman and her children. The investigators investigate, accumulate overwhelming forensic evidence which conclusively proves that the maintanence man did it and...he goes to trial, and the jury rules "not guilty." Why? Because the defense attorney puts our guy on the stand and he starts talking about how he used to be a bad guy, but he's changed now. He's training in a seminary to become a protestant pastor! "Boo hoo! Boo hoo! Look at me, so innocent!"
Three obviously guilty people got away. They shouldn't have. But they did. All because of the way that our broken system works (or doesn't, for that matter). If we had a Judge Dredd style criminal justice system, things would have turned out much differently (and more justly, for that matter; all three parties would have received the just sentences that they deserved). In all three cases, the guilt of the accused was perfectly obvious. A trial by jury was completely unnecessary and, not only that, its very existence only served to
circumvent justice.
At least in the first two cases, the police officer should have been able to serve as judge, jury and executioner. Those criminals should have been arrested, judged and sentenced on the spot.