Several good questions here .. is it according to the Torah?
My understanding is that we do not require non-Jewish system to adhere to specific norms, such as what would a beis din decide for a non-Jew. As long it is trying to do justice. Jury system, as democracy, are obviously not the best decision sharpest mind can come up with, but it has the value to protect citizens from abuse by the powerful people. Interestingly, even in Nazi Germany, juries were acquitting some of the people who were caught listening to “enemy radios” and such.
With many social issues, chachomim proposed a solution and then judged it by results, and changed the system further as needed. So, here, we can judge the system by results – and they are reasonably good currently, I think, in terms of deciding guilt. One can argue with the prison system that does not seem to have any value beyond isolating the criminals. But overall, as long as the system tries to punish guilty and protect innocent, we should participate.
As to citizen ethics and morals, both jury and elections hinge on them. So, it makes educational system and media relevant to us. If population will get into communist or Nazi ideology, it will affect us directly.