We have a jury system not because jurors are are necessarily wiser, more educated, or innately smarter than the alternatives (judges, kings, standing tribunals, viziers, etc.). By and large they almost certainly are not. We have juries because they are safer for those of us without power (the 99%, to use a phrase that has become all too hackneyed in such a short time) than the alternatives.
The Zimmerman case is a classic example. The prosecution was not based on the evidence against Zimmerman. It was based on the politics of race. The State Attorney should never have brought the case. She had no hope of proving beyond a reasonable doubt that Zimmerman committed murder, but she was afraid to do the right thing. The jury protected Zimmerman from her abuse of power. It just that simple.
To protect people like Zimmerman (and you and me) from the power of the state we have to put up with a few OJ-type juries.