Earlier quoted context omitted.
It's obvious that the people on the grand juries are not qualified to asses anything and it's an archaic system not employed by any other country This is an odd statement. It's well known that prosecutors have much greater latitude in what they can present as evidence AND the hurdle for proceeding with criminal charges is much lower. The other option is to leave decisions to charge somebody up to the prosecutors them…
Grand juries don't seem to correct the most egregious errors in either direction. Consider the famous assertion that a prosecutor can get a grand jury to indict a ham sandwich. On the other hand, consider the recent non-indictment of Darren Wilson. How often do grand juries defy the prosecutor's wishes? I certainly agree that a check on prosecutorial discretion is badly needed. But the grand jury system doesn't seem…
The high rate of indictments, of course, doesn't prove that the grand jury system doesn't act as a check on prosecutorial discretion. An AMA study found that the largest health insurers reject 2.7-6.8% of all claims: http://www.politifact.com/truth-o-meter/statements/2009/sep/.... Does the low rate of denials indicate that insurers' claim processes are an inadequate check on fraudulent claims? By your reasoning, it does.