Let me put this in simple terms. America's laws of justice are as good as any other. It reflects our (American) values and ideas of how society should relate together. However, the legal system aspires to deliver justice but in reality does not accomplish its goals.
As an attorney in criminal justice for many years, I had the opportunity to observe the administration of justice firsthand. I remember we always told our clients that "if you are looking for justice in a courtroom, you won't get it". What you get in a courtroom are human attempts to apply the existing law, good or bad. "Justice" differs from courtroom to courtroom, jury to jury. It is clearly influenced by the political concerns of the decision maker(s). Most judicial officers are appointed rather than elected. This means they must be well politically or they will not be appointed. The appointments are not by merit judged objectively, but more about how a particular Judge will vote in accordance with the philosophy and ideals of the appointer.
Judges are also much concerned with the continuation of their jobs. After being appointed, they are up for election in usually 6 years. If there are no major screw-ups, and the Judge stays within the reasonable expectations of the he/she will likely run unopposed and be reelected. If a Judge deviates from normally accepted societal behavior, he/she will attract attention and be exposed to allegations of incompetence, activism and the like. A Judge is "very conscience of this when rendering decisions.
A majority of Judges, on all levels, started out practicing law as prosecutors, hard line enforcers of the law, prosecuting every case unless its clear they won't win. And justice is all about winning. that's what defines lawyers, prosecutor and defense alike. The law says a prosecutor is the has a legal and moral duty to decide if a case rates prosecution or not. Bur that's not how it works. However prosecutors who have "put in their time" as District attorneys and ascend to the bench with their pro-prosecution in tact. The public likes the "tough on crime" mentality, sometimes irrespective of the evidence. And if you are tough on crime, you will likely be appointed or reelected.
Therefore the predilection of the Judge, and the possible political and societal fallout greatly influences his decisions when seen in a panorama of his career. Most Judges are to egotistical to admit this, but then they cannot be too good at psychological investigation in this world of black and white issues and laws. The Bible says "man judges by outward appearance, God judges by the heart". It most certainly never gets to that point in our justice system. As we always said, I repeat, "you don't get justice in a courtroom". What you do get sometimes is the results of prejudices, bias, upbringing, inbred thinking and snap judgments.
Our justice system, from courtrooms to jails to prisons are so overcrowded how could you get justice? The courts simply don't have the time to administer it. The prosecutor and public defender arrive in court with a stack of files under their arms that they have never looked at previously. The Judge has the same stack of files in front of him, unopened. The "justice" system becomes a place where the object is to resolve cases and clear the courtrooms just so it can be done all over again the next day. The pressures on a defendant to resolve his case, guilty or not, rather than exercise his constitutional right to a jury trial are enormous. Most Judges make it well known that if a defendant goes to trial, and loses, that the penalty will be much stiffer than pleading guilty today. And nobody likes a trial, from court clerks (they have to work all day), same with Judges, same with bailiffs and court reporters. Even defense attorneys know a trial will take them away from their offices where they can sign up new cases and take additional retainers. And boy does the work pile up when you're in trial.
Well you say "that's human nature". That's true and always will be. But this is a critique of the American justice system which includes how it really works. You can theorize and philosophize about justice as much as you want, but the fact is it is not really being administered despite rhetoric to the contrary. And a defendant, who may or may not have done the act(s) alleged, is still entitled to real justice.
Still, after saying all that, over the long run, justice is probably done in the majority of cases. That would be OK as long as you aren't the defendant who needs an objective analysis in HIS case. Everybody involved does SAY that is better for a 100 to go free than one innocent man get convicted. Everyone may say that but in reality, it doesn't work that way. As a matter of fact it is never given a thought; the thing that is given a thought is: "let's get rid of this case" so we can all go home early.