Originally Posted by Thor 2
Your anecdote establishes the unreliability of witnesses more than it establishes the unreliability of jurors.
Having sat on a jury myself (and been foreman since no-one else wanted the honour), I can say that the jury is not asked to assess the evidence, they are asked to assess the arguments. The evidence is there to support the arguments made by the lawyers, and prosecution and defence will present different evidence.
The other thing is that jurors are not asked to interpret the law. In fact, we were sent out to the jury room for a considerable time while the lawyers debated about a specific interpretation of the law (specifically, whether it is lawful to use reasonable force to resist an unlawful arrest (turns out, it is)). When we were brought back to the courtroom, the judge gave us the interpretation of the court and we went on from there.
So my answer to your question is the same as Churchill's answer about democracy. Trial by jury is the worst justice system, apart from all those others that have been tried from time to time.