Earlier quoted context omitted.
Look up studies on the reliability of witness testimony if you want to get really scared on how courts run.
Even forensic science can be used questionably. Really, once you're in the court room it's entirely rhetoric and fudge-factor.
I agree with all the skepticism of particular types of evidence in this thread including witness testimony and forensic evidence (I'd also add even confessions to this list). But this rather extreme conclusion doesn't follow. Evidence can be uncertain and hard to interpret, but still lead us to truth. You just need more than one data point.
In a typical criminal trial (assuming the defendant is guilty) the prosecution generally will not hang on a single dubious piece of evidence. They will often assemble a veritable mountain, if they can, because they know that a competent defense attorney will make sure that the jury knows better than anyone the various ways in which evidence can mislead.
This is not to say that everything is rosy in the criminal justice system, and that juries always get it right. There are lots of big problems: Juries are often mysterious and unreliable. Defense attorneys often do a bad job (meaning, among other things, that the prosecution can get sometimes get away with presenting a weak case based on shoddy evidence). And, lest we forget, huge numbers of criminal prosecutions end in a guilty plea, and never go to trial in the first place (sometimes for good reasons, sometimes for bad).
But I want to push back on the extreme notion that the outcome of every trial is all about rhetoric. Sure, it plays a role and some cases are better than others. But I've never seen one that was "entirely rhetoric and fudge-factor." (I'm sure it happens, but not often enough that I've ever seen it.)