I assume the number you're referring to is from Judge Jed S. Rakoff's editorial: http://www.nybooks.com/articles/archives/2014/nov/20/why-inn... ("How prevalent is the phenomenon of innocent people pleading guilty? The few criminologists who have thus far investigated the phenomenon estimate that the overall rate for convicted felons as a whole is between 2 percent and 8 percent...")
So between 92% and 98% of the time, plea bargaining gets things right. The "beyond a reasonable doubt" jury trial standard is unlikely to be more than 95% and is in practice probably 90% or lower: http://federaltaxcrimes.blogspot.com/2014/09/proof-beyond-re.... So if the 2-8% error rate is correct, it's not clear that plea bargaining leads to more innocent people being convicted than jury trials.
Moreover, it's unclear to me that you can do much better than 90-95% accuracy. Say you set the threshold at 99.9%, only convicting when the proof is overwhelming. What would be your rate of false negatives (i.e. where you let a guilty person go)? And how would society react to that? There's a false negative rate beyond which people will push back on the court system as being too lenient on the accused. You can already see this in areas of the law where proof is difficult. For example, I think the crazy administrative proceedings for rape cases in college campuses arose, in part, because of the difficulty of holding guilty people accountable in the court system.
So between 92% and 98% of the time, plea bargaining gets things right. The "beyond a reasonable doubt" jury trial standard is unlikely to be more than 95% and is in practice probably 90% or lower: http://federaltaxcrimes.blogspot.com/2014/09/proof-beyond-re.... So if the 2-8% error rate is correct, it's not clear that plea bargaining leads to more innocent people being convicted than jury trials.
Moreover, it's unclear to me that you can do much better than 90-95% accuracy. Say you set the threshold at 99.9%, only convicting when the proof is overwhelming. What would be your rate of false negatives (i.e. where you let a guilty person go)? And how would society react to that? There's a false negative rate beyond which people will push back on the court system as being too lenient on the accused. You can already see this in areas of the law where proof is difficult. For example, I think the crazy administrative proceedings for rape cases in college campuses arose, in part, because of the difficulty of holding guilty people accountable in the court system.