There are very good reasons most court cases rely on juries for ultimate judgment rather than a sitting judge. The overall aim of the US Constitution is to limit the power of government and maximize the power of ordinary people.
In this context, the Founders established the Sixth Amendment to the Constitution to cover trial procedures. While there has to be some sort of standard to enforce proper guidelines as with most aspects of everyday life, the Court Judge still has to recognize and respect reasonable limits on his or her power. The courtroom jury reinforces the principle of power ultimately residing in the people, not the government or an agent thereof.
As with the prescribed function of all government, the Judge serves to make sure Constitutional procedure is followed in making sure the jury understands and follows guidelines that serve to facilitate the cause of justice. However, the judge is not allowed to simply overturn jury verdicts, save in civil cases that are not a matter of criminal law or to overturn a verdict of “Guilty” whenever the Judge finds there is some miscalculation or misunderstanding of the law on the jury’s part. A “Not Guilty” verdict will always stand in order to safeguard the rights of the accused.
It is not difficult to fathom the reasons for limiting the power of a Judge and subjecting it to review. Ultimately, a Judge is just another human being with biases and preconceived notions just as any other. An attorney who is aware of such biases that may be a factor can always call for a such a Judge to recuse him/herself, but that may or may not be successful. A Jury composed of a broad range of ordinary people is therefore important as a counterbalance to that possibility.
Without going into statistics, it is also not unknown for some Judges to yield to some sort of bribery to lean and direct the case in such a way so as to achieve a particular outcome. Having twelve random people who also certainly have differing views of various aspects of a particular case go a long way in hindering, if not outright defeating such a scenario.
Of course, there are down sides to having a Jury trial as well. In a criminal case, there are occasional hung juries that result. Chances are the Judge will have the jury keep deliberating in hopes a deadlock can be resolved, but such an action goes is costly and sometimes ends up with the prosecution having to decide if the accusation is worth the additional cost of a whole new trial. And of course, that is quite detriment to the Constitutional goal and ideal of a “speedy trial.”
In matters of Civil Law, where the deciding evidence need only be slightly more convincing than the opposing, ordinary citizens might find themselves confused from the difficulty of understanding the minute detail. Also, such inexperience may make biases easier to act upon given the lesser standard of evidence. As stated earlier, judges can overrule a jury verdict in such cases, but when that happens, it would seem to be a logical conclusion that a bench trial would have been the better option in the first place. At least the final ruling of a judge will be open to review when one or both sides find it warranted. Like the earlier example of calling for a Judge to recuse him or herself, appealing a court decision is not assured of success and the party may find repeated efforts to make an appeal not an option due to cost.
When all is considered, Juries still seem the best way to safeguard one’s rights when a party in a court case. One certainly wants to achieve the greatest degree of impartiality possible, especially when accused of a crime and possibly facing loss of freedom and perhaps even their lives.